I wouldn’t personally say that it has anything to do with fatigue or oversaturation. I think the reality of it is that the majority of these movies have no heart, feeling, or direction. The obvious counter example to this trend is the Guardians of the Galaxy films, all of which are dripping with heart and are obviously thoughtfully crafted, and are all around good moving despite being in the MCU. If this universe of films were all given the same amount of care and thought as those films, I think they would all be successful. But alas, capitalism.