a lot of my thoughts have been covered by dodmen, lax, and teddeh, but i will try my best to provide some other insight.

as a disclaimer, i've never been a fan of using sneasel myself, i've maybe only used it on a few teams and i've only used it once in any nu tournament. while it is still rather common in ladder and tournament play, i do think there is a big distinction with sneasel compared to other common pokemon; that sneasel is a pokemon that can be put on a number of teams, but it's not as commonly successfully fit on teams. i feel like a problem is that sneasel can be rather suspectible to giving up a number of free turns to opposing teams, and teams that are not well-equiped to limit the opponent's opportunities from these free turns can make sneasel a bit of a liability on some teams, so i don't necessarily think fitting sneasel on teams is as easy as some may make it out to be.

discussing more on free turns that sneasel gives up - while i do recognize that sneasel can be extremely potent if executed successfully, this isn't always the case, and if it clicks the wrong move, it is very susceptible to giving up free turns to the opponent which can put sneasel users at a disadvantage. i find that personally my play versus sneasel that more often than not that sneasel ends up giving away free turns to the opponent rather than being threatening offensively, maybe it's just a matter of my playstyle and builds, but i don't really find sneasel difficult to play against, even when sneasel isn't really a pokemon i take into account while teambuilding, unlike other pokemon like vanilluxe, heliolisk, venusaur, incineroar, klinklang, etc. and of course, there are a good number of checks that still exist in the tier (one of which being slowbro, which is extremely common in the tier and can check sneasel fairly consistently), which can rather effectively limit sneasel from being extremely effective, while also allowing opposing players to gain free turns vs sneasel, which i find, more often than not, the opposing player is able to take advantage of, even against some better constructed sneasel teams.

of course there is the issue of how healthy/unhealthy sneasel is when taking into consideration of whether it should be banned or not, as i mentioned, i do personally find that sneasel ends up being deadweight quite a bit, but of course it can be problematic if it is able to execute moves correctly. it does help balance teams a lot in being able to eliminate a number of threats which would otherwise be very threatening to balance like cm delphox, heliolisk, vivillon, jynx, vanilluxe etc. there are still other threats to balance that exist that sneasel can't handle as effectively, like incineroar, scrafty, and malamar. i think a problem with removing sneasel from the tier may be that teams which rely on sneasel to remove these threats will have a more difficult time trying to be sufficiently prepared for these threats, along with the other major offensive threats in the tier. i fear that pokemon like venusaur, vanilluxe, vivillon, and heliolisk may become too threatening for the tier if sneasel is banned, and in the essence, reduce diversity in the tier, contrary to what seems to be a common belief among those who want sneasel to be banned, as i think that as these threats become more powerful, teambuilding options may be constricted. also of course, assault vest slowking will be very annoying to play against since it won't have to worry about dragon tailing into sneasel, which can make future sight quite threatening, as it continues to check a number of special attackers in the tier. xatu too will be even more annoying that it already is to play against and try to setup hazards against.

something minor, but i think the rise in effectiveness of sd incineoar, especially with intimidate makes it more threatening to sneasel, more so than emboar which more commonly ran scarf so it had fear in losing its item, unlike sd incineroar; so i'd say sneasel has a more difficult time in being consistenly effective with incineroar being more common now, as compared to emboar meta (i'd also say z incineroar is better offensively than z emboar was). also hazard removal as equally as easy for an incineroar user and a for a sneasel user; it's still effective in consistenly checking sneasel multiple times in a battle, so arguing that incineroar isn't as effective as check because rocks are up is a bit silly.

so overall, i do not think sneasel is inherently broken in the essenence of being a consistently threatening offensive threat, nor do i believe it to be unhealthy or restrictive to teambuilding as some might say, nor would banning it help increase diversity in the tier.