What I'm responding to, though, is the idea that the game is trying to present him as a "good guy". I'm saying that everything about Xehanort's motivations presented in all these works is consistent with him being a horrible person.
Old Man Xehanort IS a terrible person who personally screwed over everyone including his younger self, I'm not trying to give some grace to people here but I think what people mean when they say KH3's ending portrayed him as a "good guy" is that the ending he got didn't seem particularly in line with the way his story had been presented up til then.
Like up til then, every villain gets a comeuppance, and they get endings that don't vindicate them at all. I am again - NOT saying that KH3 vindicated Xehanort, it was obviously not meant to come across as that, but when you compare his death to literally every single other villains death, it's a little undeniable that it's a bit.... neat....
Like, it feels a bit icky that he gets to have a relatively civil moment with Sora, and that he gets to regress to a time when he was an innocent and get beamed up. Sure - that ending is not satisfactory to Xehanort the character - but its also not very satisfactory to some of the audience themselves.
Nobody's saying go Mortal Kombat on him, and that's really silly when these arguments are portrayed like that, like I'm sure Nobody is truly thinking that's what we want. But what I am saying, and maybe others too, is that lesser villains in the same series have had vastly different endings in terms of tone, and KH3 sort of broke the mold for what we expected of the most heinous villain.
I don't think all that fluff was necessary tbh, it was almost like giving Xehanort a chance to come to peace with his ending. I think he should have got to be panicky and try to come to the realisation that this was it - his final failure where there's no coming back.
We NEVER got the chance to see Xehanort actually be on the ropes for real, this guy always had a contingency, he always found a way. I think it personally would be more impactful for him to die still trying and then finally realising at the very end that there was no way out for him anymore. The unflappable villain who's been pulling strings for a decade finally runs out of gambits. Idk, maybe you guys will say its out of character but I think that would certainly hit ME more.