First, there are always people who say these things. "They've milked this. They've milked that." It's hardly an original argument and it has been around for a
long time. People have been claiming that Hollywood is unoriginal for decades, insinuating that it was at some point original.
Second, they are not facts, just opinions.
Third, if opinions had a valid impact on the box office, Michael Bay would be managing a Burger King instead of making his trademark bloated, obnoxious movies.
Fourth, saturation is an illusion. What we are dealing with are people who can't see past the major trends and only pay attention to the most marketed films. They look at the 8 or so biggest films of the year, ignore the dozens of others, and whine,
"this all Hollywood makes!" and then claim they are not being sheep like everyone else who see these movies, when in fact those are the only movies they willingly pay attention to. There's a lot more variety out there if you actually look for it. Of course, generally these kinds of people also claim superhero movies are devoid of intelligence, yet when they see a film that is bold, thought-provoking, etc., they claim it's boring. Funny how that works.
Finally, these movies (or at least a majority of them) are still making money. It's also worth noting that they have taken risks with a lot of these major films. Civil War is pretty subversive at times and has a final act that I guarantee would have been changed had the film been made years prior.