Bullshit, WandaVision and Ms Marvel came out two and one year out from The Marvels. None of those movies are doom are because the main cast didn't have annual cameos. That's never been an issue for literally any franchise ever!
I swear to God this board has the most ridiculous explanations for why things will and won't bomb. cap 4 would not magically be a guaranteed billion if Sam showed up in Eternals or whatever you want.
Everyone is insistent that there shouldn't be homework, but also everyone needs to constantly be making new appearances, but only make sequels to successful movies, unless those sequels introduce new characters, but they also can't involve returning characters making appearances after their previous appearances. People are simultaneously claiming the Marvels bombed because the characters hadn't appeared enough before and then turn around and say that the returning characters caused it to bomb!