The MCU has run out of steam after they got away from the A list heroes. It’s not that B- or C- list characters can’t do well, it’s just that it takes a talented writer/director to do it with a good movie, and Disney/Marvel just isn’t capable of getting that consistently on their own, they’re too safe & corporate. They’re just trying to recreate what made the original MCU run successful, but we’ve already seen that. I don’t know that there’s necessarily “superhero fatigue”, though trends in movies & pop culture come and go, that’s inevitable, but for me it’s more been “bad writing fatigue”, I’m just sick of their lazy ass shit writing, it’s insulting and I’m tired of being treated like that by the MCU.
James Gunn did great with Guardians of the Galaxy. I’m not sure many others could’ve pulled it off as well.