I think you've hit the nail on the head here. This is a very sad, very public case of mental illness combined with the paradox of success. There's no way, healthy or not, that he wouldn't think he knows better than everyone else for exactly the reason you describe. Anyone in his position would be fighting back the naysayers. The major difference is that Kanye has had enough failures and stumbles now that his whole "god" and "GOAT" persona is publicly falling apart and he doesn't know how to handle it. The mental health issues are just exacerbating his inability to reconcile his personal ambitions with reality.

Just think about it... if you've been a success for so long and suddenly aren't, who would you blame? If you didn't say anyone but yourself, you're not Kanye.