"Superhero MOVIES" is a sub-genre of the action genre, with many, many, many possible genre mash ups.
And boy have we seen diversity in that genre! I dare say that Superman:The movie and The Burton Batman were what comes closes to "comic book movies". "The Shadow" comes to mind, the old Flash TV series. Those were so close to the source material. And nowadays we are seeing "enhanced" versions of those heroes, sometimes very remotely connected to the source material. Most times not bad. But I dare say that todays movies have more depth to them, character wise. Good cinema, most of the time. Good stories, just what
Inquisitor Peregrinus pointed at. That is what is important. If the story is bad it does not matter what movie genre a flic belongs into. The same is applicable to the general execution of a movie.
People aren´t tired of rom coms, horror movies, thrillers, drama in general. There have been genres in movie history that have been more popular at times than others, but apart from very specific niché-y sub-genres I cannot come up with one genre that completely died out. Superhero movies have always been around, more or less. Every other year there was a superhero movie, and I think that if the technical hurdles hadn´t been as tall as they were in the past, we would have seen more of them, especially in the 1970ies/80ies.
I think it is more about developing a personal dislike, e.g. due to age or a shifts in general interests, that make people turn away from one genre or the other. Those may be the first to start some kind of a trend, and I wouldn´t dare to say that superhero movies are here to stay, but atm I do not see a fatigue among the general movie going audience.