I think it's mostly d list character fatique. marvel got cocky when guardians was a hit and now think any comicbook property can translate to sales.
Spiderman and Batmans recent film both did well and were well received. (stories weren't any better than any other super heroes despite what gunn is saying.)
shazam, black adam, antman and all these other side characters are the ones flopping.
as much as people like the say that the avengers a c list, individually they are, but they were also the first team up film of muliple solo characters.
Realistically, Marvel should build up hype again by focusing on either X-men, FF4, or make Daredevil and Spiderman their primary focus going forward.
Blue Beetle is going to flop hard, the marvels will flop too, madame web is going to flop, guadiarns 3 will show signs of diminishing returns but might do alright since its being marketed as the last gunn film. thunderbolts and cap 4 will both do antman 2 numbers.
After End Game they should have took like a year off.
Then they should a started with the X Men, like they did with Iron Man. Just a dope movie with the Original 5. No Wolverine til like part 3.
Same build up like they did with Iron Man etc. So like: X Men, X Force, Apla Flight... whatever different "solo" films that all come together in a big event.
The real problem with Marvel and Avengers is that Endgame was the end of that story. We really went from Thanos to Mysterio.. Just let the Avengers entire series rest (by Avengers I mean ALL those mfs coming out of portals behind Cap in the final fight).