It's not superhero fatigue or franchise fatigue. It's bad writing fatigue. Seriously, I don't know why Hollywood keeps choosing terrible writers for huge projects, but as long as they are doing that they are going to keep getting what they deserve.
And speaking of huge projects, from what I've heard Indiana Jones and the Dial of Destiny cost $295 million to make rather than 250. And that's not counting publicity and marketing, which brings it to 400 million if not more. That means they need to make at least $800 million to break even. No matter how you slice their opening weekend, they are in huge trouble. And given that Elementals and The Little Mermaid both bombed hard along with most other Disney movies of the last few years, I'd say that Disney is in serious trouble too!
On the other hand, Guardians of the Galaxy 3 was rather well written, and from what I've heard it did rather well at the box office. Which is just more evidence that if you have a decently-written film the public WILL go and see it. We're just avoiding crap, that's all.
I'll go out on a limb and say that hauling poor old Harrison Ford away from his bong and forcing him at the age of 80 to make shitty movies is tantamount to elder abuse. As for The Flash, coddling wannabe cult leader and mental defective Ezra Miller was just the icing on the cake. The movie was just badly written.
Frantic last minute reshoots and rewrites are a dead giveaway that something is seriously wrong with a production. But that that is happening so often in Hollywood in the last several years is clear evidence that Hollywood itself has completely lost their way. I don't know if they can right that ship, and to be honest I don't much care. If they won't provide people with the good entertainment that they want, eventually somewhere else will. Maybe Bollywood or China.