A little late but I wanted to provide actual tangible insight from someone who's watched professional tf2 for years. I'm not much of a b4ndit and i hardly watch his streams or videos but im always watching matches and taking notes. I see a lot of people talking about how many hours he has, which is a huge factor in his main calling, but no one really says much more than that.  so I’ll answer this question more accurately. This will be a long post sorry.

Anyways the answer is essentially all of the above that you suggested.. and more.
I’ll speak on his DM first since DM imo is one of the more overrated qualities in 6s. It’s important don’t get me wrong, especially on flank scout and roamer positions where you usually need to rely on good aim during isolated situations, but it is not the most important quality in a teammate (there’s playcalling/maincalling, gamesense, team chemistry, other mechanics). But I’ll speak on his DM anyways, since an alarming amount of people seem to disregard his DM, seemingly purely out of hate (and his scout playstyle, most mostly hate lol), but we should all agree that b4nny the player is different than b4nny the person. He doesn’t have the absolute best DM in invite, but it’s up there. Like way up there. There are plenty of VODs and YouTube videos out there that perfectly encapsulate his DM on every 6s class. Since he’s most recently been playing scout for the past several years (with the exception of RGL s13/16), I’ll mainly focus on that. It’s hard to rate his raw DM due to his playstyle on scout, as he plays a mama bear type of role allowing him to consistently be in close proximity to his teammates and receive heals, but in those occasional isolated instances, he wins those exchanges way more than he loses them. As much as I hate factoring MGE skills in when grading players, I think the DM department is an exception because that’s exactly what it is, deathmatch. B4nny consistently out-MGEs top invite scouts, and can occasionally beat the more prestiged DM players. There’s a video on YouTube that’s just about an hour or two of b4nny MGEing jay, who’s considered to be the most mechanically skilled and gifted player ever (and I would agree), and though jay wins a majority of those scout v scout matches, b4nny pulls out a handful of wins, some back-to-back, even winning a majority of his soldier v scout MGEs vs jay. He’s also beaten yomps on scout v scout in MGE several times (and iirc you can see one of their matchups on b4nny’s i63 showmatches VOD). I’ve never seen b4nny MGE clockwork (though probably happened in private), but I have seen him MGE slemnish (“the Omega Eye-test [of DM]” -botmode), probably the best DM scout to touch NA imo (outside clockwork if you’re including DM “for their era”) and the best DM scout he’s ever MGE’d. I remember watching some of these MGE’s live and expecting b4nny to lose, which he did, but he did hold his own pretty well, posting an avg of 13-15 kills per MGE against slem, occasionally coming away with a few wins here and there. He’s also imo got the 2nd best movement of all time (other top invite players have said this about him as well) as a scout (1st before jay started pounding on scout), which definitely helps factor into DM. My point being is that b4nny can sometimes do well against proclaimed “DM beasts” (yomps, jay, slemnish, branslam, etc. for EU readers, their DM is comparable, and in some cases better, to that of Thaigrr), even edging some of them out. While his DM on scout isnt Top 1, it’s definitely in the Top 10, and better than the majority of invite scouts, so in no way is his DM there mediocre. His DM on soldier is roughly the same, maybe a bit worse (not a knock). His DM on demo is Top 2-3 imo. There’s a reason he’s called Pipe Jesus. So yeah he has beast DM. On to the next topics.

Brain. This is Grant’s strongest suit and the main reason he’s the GOAT. For the sake of simplicity and keeping this already long post as short as I can, I’ll tie that into teamwork and map knowledge here. B4nny is easily the smartest player, and that can be seen in several facets of the game, primarily in his playcalling, decision making, teamwork, and map knowledge. He’s the best playcaller/maincaller (as also agreed and said by top invite players, both NA and EU) the game has ever seen, and by a pretty wide margin. He has such a great understanding of the game. It’s safe to say he can beat any team, given equal (and in many cases subpar/inferior) teammates and thorough planning. He can read plays long before they happen, and use that knowledge to help his team better position themselves and adjust when needed. A problem many maincallers run into is lack of providing information or providing too much (useless) information, cluttering the brain. B4nny does none of this, almost always makes the best possible calls fit in the scenarios he’s given with the cards he’s been dealt in his teammates. He can call how to play any situation with near perfection, whether it’s against aggressive DM-heavy teams such as EVL, Witness, and Ascent, or slower-paced smarter and methodical teams such as Se7en, he can adjust to it all. And he has, coming out with a gold medal in every one of those instances, some of those examples having better rosters than b4nny’s (I will speak more on this later). Because of his phenomenal playcalling and his ability to preserve teammates for several seasons, he teams are always selfless and cohesive, with THE best teamwork in invite, and this can be seen in basically every iteration of FROYO. In many cases, not only is his presence why the teamwork is good, but I’ll go a step further and say his presence and abilities also play a huge factor on why his teammates play better, and why some of them even have a name for themselves. To put it bluntly, he’s made dozens of players’ careers. Every iteration of FROYO is always in contention for First Place, whether it was HRG or Froyotech, regardless of if the era was the Golden Era, the Dark Era, or the RGL Era, he’s a huge threat. Just like lebron makes his teammates better, the same can be said for b4nny, and in no way am I saying his teammates are crap without him. What I AM saying though, is they need him way more than he needs them. You’ll hear haters say stuff along the lines of… “But X and Y were on his team”. But somewhere down the road, you’ll find instances where X and Y are NOT on his team, and he’s still coming away with gold. To go further again, in some cases X and Y are playing AGAINST him, and b4nny STILL prevails with the W, even with all odds stacked against him (will speak more on this as well). Out of the several dozens of iterations of his teams, with players coming and going, one player has always been there to bring home gold, and that’s b4nny. Coincidence? I think not. As for map knowledge, while you won’t see him abusing gimmicky high spots or hiding spots as an individual, as a team player- yes he has incredible map knowledge, which is why his and his team’s positioning is usually so great. They’re historically the best Product team ever, and pound on so many other maps.Mechanics. As a scout, A++. As demo, solid. As a soldier, not a T6 jumper by any means, but decent, though he is not in the conversation of best soldier mechanics like the sorts of jay, Laz, marmaloo, kaptain, etc etc. Invite-wise he has middle-of-the-pack mechanics on solder, upper-echelon mechanics on demo, and exceptional mechanics on scout. Overall I’d give his mechanics a combined 7.5/10.

Now let’s talk turkey. Results in regards to his team compositions, as well as my runner-ups for the GOAT and why they fall short of GOAT status. I’ll save the numbers for my conclusion. When his team is better on-paper, he wins 99% of the time, and a lot of the time his team IS better, leading to some people (a small minority but still prevalent) using that as a dock on his GOAT status, but I’m going to put these conspiracies to shame. First to get this out of the way, it should be obvious your team needs to be amazing to see results. That’s a given in every e-sport, sport, and team game out there. Saying he only wins with good players is not at all a hit on his reputation, and I’d go as far to say it only helps his case. There have been several instances where his teammates branch out somewhere else, leaving b4nny with a mediocre lineup just to win again and prove that he is not part of a system; he IS the system. Let’s go over just a few of the many instances this has happened. ESEA Invite s21. Froyotech (clockwork, Freestate, paddie, b4nny, Muma, ninjanick) had a 4-0 SWEEP in the Grands against the much more talented (on-paper) roster in RONIN (Shrugger, yomps, Ma3laa, rando, Bdonski, phorofor). RONIN had the better scout duo, demo diff, and med diff, and I’d almost put Ma3laa + rando head to head with b4nny + paddie. “Clockwork carries”? Hmm ok. Literally next season, they lose clockwork and pick up a rusty TLR who had been on a 1-year or so hiatus from TF2 altogether. They manage to take phorofor from RONIN, only for RONIN to pick up Nursey. Froyotech (Freestate, b4nny, paddie, TLR, Muma, phorofor) effectively downgraded their roster while RONIN (Shrugger, yomps, Ma3laa, rando, Bdonski, Nursey) upgraded theirs and still lost in the Grands to FROYO, albeit fortunately not a sweep this time for RONINs sake. How about b4nny’s favorite talking point towards player legacy: international LANs. Rewind I. Main stage. Grand Finals. Froyotech (b4nny, Freestate, blaze, paddie, habib, Nursery) vs Se7en (Thalash, Starkie, AMS, Drackk, alle, Raymon). Again, FROYO were the underdogs here, statistically speaking. Se7en overall had the better scout duo, better soldier duo, and med diff. Thalash said it himself in an interview (iirc still available on YouTube on the official Se7en channel), that he was shocked of the lost due to how strong their roster was. Even wins don’t have to be impressive. Some of FROYOs losses are impressive on their, just based off how well they performed against their competition. Let’s start with the dreaded i58 international LAN that ended in #3rdPlaceB4nny plastered all over TF2 subreddits and TFTV. FROYO with arguably  their worst roster ever (pre-RGL s10) lost 2-1 in the Upper Bracket Final against Crowns (Hafficool, Starkie, Drack, kaptain, Spudd, Raymon), which outclassed FROYO in overall scout duo, soldier duo (this one by a HUGE margin), demo, and med. Even though FROYO lost, they kept it way closer than they should’ve on Crowns’ part, winning the same amount of rounds as Crowns and forcing them to win via a golden cap. Similar can be said for the Lower Bracket Final that followed. Again, Fult Tilt (Thalash, astt, Mike, Silentes, alle, kos) had the better soldier duo (HUGE margin again), better demo, better med, though I’ll give a slight edge to the FROYO scouts as a duo. FROYO took the first map, forced a golden cap in the second map in a loss, and lost the third map by a single round. Despite this loss, it was also close as all hell, and we could be looking at a VERY different LAN outcome had FROYO had one of their more competent rosters, not even necessarily one of their better ones. That FROYO roster isn’t even touching 5th place had b4nny been absent. Also to stick it to Full Tilt fans who were more fixated on b4nny losing than their team winning: nice job blowing a 2-0 lead in the Grands. Anyways, let’s look at a couple more losses that still display the greatness of b4nny. Next i-series. i61. Not an international LAN however, since the only American present was b4nny. No FROYO. Just b4nny joining a brand new team off a whim, with teammates he’s never played with or even interacted with and almost never played against, with a totally different playstyle than NA he needed to adjust his teammates to, took a loss to the best roster to ever come out of EU (Thalash, Starkie, kaptain, Drackk, kaidus, Raymon. Yes, better than ETF2L s32 Se7en) who outclassed SVIFT (the EU team b4nny played on) on scout duo, soldier duo, demo, and med. SVIFT first lost in the Upper Bracket, losing 2-1 maps, only a round shy on map 3 from moving to the Grands from there. Once making the Grands from the Lower Bracket, they took the first map by a round, and lost the next three maps, each by only a single round as well. Had b4nny not been on a last minute EU team with no familiar teammates with no familiar playstyles, we also could very well be looking at something different. Fact of the matter is, 1) those wins from EU are not to gloat about. If you’re that good, you should not be cutting it that close, especially when you’re competition isn’t shit in comparison and you blow them out of the water in pure skill and 2) These losses considering all the criteria I gave, aren’t at all a knock on b4nny and actually help his GOAT case, showcasing how well and close he fought and took his teams given his lack of supporting cast, especially against these powerhouse teams. If you want an example of an embarrassing loss, look no further than Se7en (Thalash, AMS, kaptain, Drackk, kaidus, Raymon) at Rewind II. First of all, it’s important to note kaptain, who I believe to be the best pocket soldier to come out of EU, did get food sickness, though before he exhibited those symptoms, this team barely managed to squeeze past the 4th seeded team in SVIFT. They then lose kaptain, albeit still have a more than capable roster (Thalash, permzilla, AMS, Drackk, kaidus, Raymon), get SWEPT 5-0 and 5-0 by FROYO, and lose to the second seed in Ascent in the Lower Bracket, not picking up a SINGLE round in either of the maps. That’s the difference between b4nny and everyone else. He will ALWAYS keep his teams in contention, no matter how overpowered or shitty they may be.

Now let’s look at potential challengers for the GOAT status, and why they don’t only fall short, but fall MASSIVELY short from b4nny’s prestige. And I use the term “challenger” quite lightly. Really it just means who’s second and third all time.

From EU:
Starkie - imo the best player ever in EU. Very high IQ player who plays a high-risk high-reward flank style that more often than not works in his favor, allowing him to get important picks, especially during crucial moments. Definitely one of the most if not THE most clutch player ever. Immediately my mind goes to his game-sealing backstab onto kos on Map 5 at i58 of the Grand Finals on process, and his clutch Spy play onto Nursey during the Grands at Rewind I Map 5 (although ended up losing that game to FROYO). He comes in hot when his team needs it the most, and still shows up in the most important moments even at LAN when the spotlights shine brightest. I actually have him slightly above clockwork as my GOAT flank scout due to his combination of absolute clutchness both online and at LAN, incredible gamesense and good mechanics/DM. He only ever takes fights he has the edge on and picks his matchups extremely carefully when possible. Stark is also an incredible off-classer. I already mentioned a couple of his clutch spy plays at LAN, one being a game-winner, but he can also play sniper at an exceptional level, going toe to toe with insane snipers like Thalash at online or slemnish at LAN, he can compete at the highest level of sniper play. He also played medic well at i63 and plays a very good roamer. Now let’s compare him to b4nny. Both have the multiclass ability checked. While you can’t directly compare a pocket and flank scout, b4nny’s scout play has been more impactful than Stark’s scout play. Stark and b4nny both haven’t played much of their careers as soldier compared to scout, and while Starkie is a proven roamer, b4nny is also great at soldier and had the best statistical pocket soldier LAN performance ever recorded at i55. Both have limited playtime as medic, though both are very fine tuned at the position, however Stark has LAN experience as medic (unless of course you want to count b4nny medic at Rewind II lol). Stark is a better off-classer and b4nny takes the cake on demo. Overall, their multiclassing ability is pretty much split even. Where b4nny takes over Starkie is really in playcalling, team value, accolades, and longevity. Starkie hardly maincalled on Se7en, and that’s usually up for Kaidus to do, while b4nny has the best coms in the game. Due to his playcalling and high IQ plays and team composition, b4nny also has more value to his team, proving time and time again he can take a gold medal even when the odds are severely improbable, something Stark has never done; all of his teams he’s won with have been betting favorites. Accolades. B4nny has a combined 33 ESEA 6s Invite and RGL 6s Invite First Place’s to Starkie’s 8 ETF2L 6s Inivte First Place’s, and b4nny’s 6 international LAN wins to Starkie’s 2 international LANs. Longevity is an auto-win for b4nny. B4nny also has a winning record against Stark at LAN. What he can do to enter that conversation: Come out of retirement, up his maincalling game, win multiple S-tier LANs, and 25 or so more online tournaments, both with at least some exceptional degree of difficulty.

From NA:
jayhyunpae - the most skilled and well rounded player to touch the game, and the best eye test player, and much like b4nny, though through different means, he can lift *almost* any team he’s on into contention. Jay actually takes the multiclass pretty decisively. Jay’s raw talent on scout are untouchable and his movement is slightly a notch above b4nny’s. I actually think their scout play is pretty equal to one another, when taking into account mechanics/skill, gamesense, and logs. Where things start to favor jay start at his soldier. For awhile I had Mike as my GOAT pocket soldier, then eventually felt kaptain had surpassed him. Up until recently, imo jay has been crowned that spot, due to his untouchable mechanics on soldier, his incredible gamesense and DM, and how he changed an entire generation of soldiers played soldier with a spoon. By far the best market-gardener and overall pocket soldier to touch this game. Due to his limited time on demo, I can’t really consider the season he played as the class, though despite it being amazing, habib’s level of play is still higher, mainly due to his traps. Jay is also imo the best sniper of all time, better than jukebox, sheep, bo4r, and much more clutch at the position. He’s also an exceptional medic. Where b4nny takes the edge over jayhyunpae starts with maincalling. Jay is not as proven as a maincaller and he can’t dish out orders whilst micromanaging some teammates nearly at the level b4nny can. Like with Starkie, b4nny brings more overall value to his team. While jay is more flashy and dependable on his own, TF2 is a team game, and jay has not been able to carry his team to a championship, and to this day never won an ESEA title despite having amazing supporting casts (slemnish, Laz, botmode) and has yet to win an RGL title without b4nny, something b4nny has done several times without jay. Jay had a really good opportunity to get that RGL chip and had the better roster on paper to do so at RGL s10, where he played scout with branslam, had a top soldier duo in ash and artist, and had the GOAT NA demo in habib. Not only did they lose the finals 3-1, they won each of the two maps in the Upper Bracket Final against FROYOs worst roster to date by only a single round each, barely getting by while FROYO was in rebuild. Is that transcendental? Is that aura? Compared to the likes of b4nny… its an astounding no. And while b4nny could beat se7en with a worse supporting cast, jays team got swept 3-0 at i65 grands despite having (imo) the GOAT roamer, a top 5 flank scout OAT in slemnish, a top 5 demo OAT in botmode, and a formidable pocket scout in yight, though I was somewhat stunned to see them pull away with the Upper Bracket upset just to lose that momentum in the Grands. I guarantee at least two maps if not winning that i-series if you replace jay with b4nny on that team. B4nny also beats jay in head to head in grand finals 3-1 (if you include jay’s win at the 2021 DreamHack Community Clash, and 4-1 if you include b4nny’s Prolander win against him) and in overall playoff wins. B4nny has won a combined 33 ESEA/RGL first place finishes to jay’s 6 RGL first place finishes, all of which were on FROYO. B4nny again leads in international LANs 6-1 with jay’s 1 also being on FROYO. Overall, jay is a better multi-classer, but falls short in accolades, longevity, playcalling/maincalling, and value to his team.

TL;DR
Due to a combination of b4nny’s record high 33 ESEA/RGL titles and 6 international LAN wins, exceptional multiclassing ability, insane scout play, exceptional maincalling and team value he brings even when the odds are against his favor, and longevity, b4nny is rightfully crowned the Greatest TF2 player of all time.