>1- He explicitly said FGO was not to be a serious thing from the start.
Addendum: I must concede that the verbal group "explicitly said" might be a bad expression of mine, although my perspective the object phrase "not to be a serious thing from the start" is still very clear from his statements.

Sources:
https://oneofepisodes.wordpress.com/2016/04/18/fgo-tm-ace-042016/
frontlinejp.net/2018/08/15/fate-grand-order-3rd-anniversary-developer-interview-1-2/
https://ff.reddit.com/r/FGOGuide/comments/cni2il/fgo_4th_anniversary_famitsu_interview_notes/
https://oneofepisodes.wordpress.com/2017/03/22/translation-4gamer-interview-with-kinoko-nasu-and-yosuke-shiokawa-on-fgo-march-2017-part-1/

Statement1: Before the game was launched, the scenario up to Chapter 7 had already been completed, but at that point, none of us knew what kind of game FGO was going to be. For mobile games, it’s common sense to think, “No one would read a scenario this huge,” and there were people in the staff who thought that.

Statement2:  For a mobile game, we were expecting that players would be skipping the story, and that there’s nothing we could do about that.(...) Actually, up until Chapter 4 I had been supervising the scenario, but I was planning to leave the scenario from Chapter 5 onward to the writers(...). To be honest, from there, I was thinking, “this is a new Fate/ story, so it’s okay even if it no longer feels very ‘Fate/’, right?”

Statement3: Interviewer: So, for the sake of the players who read the entire story up to Chapter 4, you wanted to put in more effort from Chapter 5 onwards?
Nasu: Yes.(..)

Statemant4: At the time FGO was suggested, Nasu actually disliked smartphone games as a genre. He thought it’d be entirely not fun at all if they made one.

Statement5: To be honest, among us in TYPE-MOON, we had a phase where we expected that only 100 thousand core fans would keep playing, and that things would be okay as long as we kept those 100 thousand happy. If I had to put it into words, it was like: “Let us tell the story of some nerds. We’ll be making something fun, and we’ll die together with these 100 thousand people in the TYPE-MOON colony! Garden of Avalon!”

Statemant from Takeuchi: Takeuchi says that FGO was the first game they worked on with no goal, that they work on continuously like a serialisation, and that while the first year was fun, after three years, it is like Nasu said, tiring.

>2- He oftens express things like he was not very well confortable with how FGO went.
Sources:
https://oneofepisodes.wordpress.com/2016/04/18/fgo-tm-ace-042016/
https://www.4gamer.net/games/266/G026651/20181228023/
https://ff.reddit.com/r/FGOGuide/comments/cni2il/fgo_4th_anniversary_famitsu_interview_notes/
https://imgur.com/a/LGqSRTE and https://imgur.com/a/CoQMbBu
https://oneofepisodes.wordpress.com/2017/03/22/translation-4gamer-interview-with-kinoko-nasu-and-yosuke-shiokawa-on-fgo-march-2017-part-1/

Statement1: First of all, it’s simply a lot of fun. At the same time, I would think, “hey, this would be better if it were done this way” at several places.

Statement2: I saw FGO after its launch as something like a highway left abandoned for ten years. The road is there, but it’s all covered in weeds and the asphalt and tiles are all chipped and cracked. The only reason why the players were still driving cars on it is because of the trust and investment that Fate/ had behind its name. The players put up with it because of the Fate/name.

Statement3: Nasu: Jeanne’s “True Name Discernment” is supposed to be her strongest appeal as a character, so we can’t exactly make it too powerful or completely overhaul it. So within the year, I’d like to see an event where we can go “It’s Jeanne’s turn now! Her ‘True Name Discernment’ is super strong this time!” at least once.

Statement4: With regards to Artoria Lily, Santa Alter, and Emiya Alter, it was Takeuchi’s fault. They were extraneous from a scenario perspective so it wasn’t a writer’s idea. Just Takeuchi going “I want a cute character” and “I want an Alter for Emiya”. For example, the writer’s side wouldn’t suggest an Emiya Alter since an Emiya fallen to evil couldn’t be said to be Emiya. But since Takeuchi wanted it, they rethought the matter and came up with a special case where it could be possible.

Statement5: Has Nasu ever said no to Takeuchi’s wishes? Nasu: “I reject most of them! I go, “it’s impossible so stop it”. But he won’t listen to me…”

>Concerning FGO being a chore, hence, adversarial.
Sources:
https://oneofepisodes.wordpress.com/2017/03/22/translation-4gamer-interview-with-kinoko-nasu-and-yosuke-shiokawa-on-fgo-march-2017-part-1/
https://oneofepisodes.wordpress.com/2017/03/22/translation-4gamer-interview-with-kinoko-nasu-and-yosuke-shiokawa-on-fgo-march-2017-part-2/
https://oneofepisodes.wordpress.com/2016/04/18/fgo-tm-ace-042016/
https://oneofepisodes.wordpress.com/2019/01/01/translation-4gamer-round-table-discussion-part-1-mafia-kajita-x-kinoko-nasu/

Statement1: Actually, back in 2013, I was writing the scenarios for the Unlimited Blade Works anime, Tsukihime R, and FGO in sync. If everything went as scheduled, Gilgamesh bringing Humanity’s Evils during the anime…with FGO’s climax, and a certain plotline within Tsukihime R would ideally have happened all at the same time. Alas, reality is a harsh mistress… (awkward laugh).

Statement2: First of all, as one of the writers, I write the chapters assigned to me, the interludes and all the voice lines for the Servants I wrote up, and various events that I was assigned to write.

Next, my job as an editor and supervisor is to write the prologue and epilogue for each chapter, as well as the parts of each chapter that are central to the overarching plot. For example, in Part 1, I took charge of directing Roman’s, da Vinci’s, and Mash’s lines, as well as their important scenes. For Part 2, I’m writing the lines for Director Gordolf, child da Vinci, and Sion – the whole base team, basically.

Finally, as director, I’m also in charge of making the overall schedule and suggesting the content of events, as well as edits and adjustments to various game data.

Statement3:  If they were to break it down, for the main scenarios the text would be 30% Nasu, 70% other writers, while in events it would be 80% other writers, 20% Nasu. They have to write about 500 kb of text (250,000 letters) every month. The workload when it comes to text is pretty standard for professional work but there are other things they need to do too. As he said in the 3rd anniversary interview, he didn’t think he’d have to work this much. He wants a rest.

Statement4: 4Gamer: By the way, what was your motivation while writing Chapter 7 and the final chapter?

Nasu: Well, it was definitely quite taxing on my stamina. If we also count text that I wrote outside of FGO, I’d already written 1 MB worth of text back in October. I had bags under my eyes and my face must have been unrecognizable. I had to put on a lot of facial cream, and it was only during the New Year when my face went back to normal. But I felt really fired up about writing, so I had a lot of fun.

Statement5: October and November of 2015 might have been the busiest months of my entire life, but I was feeling confident enough to say that “I’m still really young! I can do this!”

Statement6: Nasu: I see… Actually, I was feeling writer’s block around the start of January. No wonder I couldn’t feel motivated at all. Anyone who writes that much would definitely feel exhausted.

Statement7: There’s basically nothing that I left untouched. Fate/Apocrypha and Fate/Prototype: Fragments of Blue and Silver are Higashide’s and Sakurai’s own stories, respectively, so anything they do with those is okay, except for setting mistakes. But FGO is a poster game for TYPE-MOON, so Kinoko Nasu has to put in his word into this scenario. I have to harden my heart and supervise this game.

Statement8: (...)for mobile games, of course there’s a goal, but it feels more like you’re sprinting short distances over and over again. You know where to run next, but you don’t know how far you need to run after that. The only thing you know is that you have to run. Your goals change depending on the situation. And as long as there are players, the sprint will never end.