I say let the market decide if there are too many superhero movies coming out.
There was a time when the same argument could be put to Westerns. I grew up at a time when just about every second television show coming out of the USA had something to do with the West. My favorites were non-traditional westerns such as The Wild Wild West and Have Gun Will Travel. Meanwhile you had westerns at the movies such as The Magnificent Seven, The Man Who Shot Liberty Valance, A fist Full of Dollars, and The Sons of Katie Elder. Westerns, whether for television or the movies, were once cheap to make so they churned them out. Nowadays I miss a good western where growing up I tended to avoid them.
Lots of ideas could be worked around the Western just as a lot of ideas can and will be worked around the Superhero. Having a lot of films follow the notion of the Superhero could stifle creativity. This didn't happen with the Western so there is no need for it to happen with the Superhero.
In any event there is a trend for Superhero films because there are some studios that have gotten good at making them.
Up until the '80s you couldn't find a good Superhero movie or television series. Certainly nothing that reflected the wonder of the comic books. Now it is possible and some would argue being done. I hated The Six Million Dollar Man because it was neither true science fiction nor true superhero. I put up with The Incredible Hulk because it cut as close as was possible back then. I remember this '80s Spiderman film that was so boring it put people to sleep. There was also a really bad live action Spiderman television show and a truly awful Captain America television show. Imagine Captain America with a flexible see-through shield. Yeesh! The Wonder Woman television show was the shining light showing that doing a superhero show right and on a limited budget was possible. I thought Captain Nice was great fun but it only lasted one season.
In 1978 it became possible with special effects to do Superman right. The Adventures of Superman television series of the 1950s was entertaining enough but it never really did the comic books justice. It was, however, imaginative with those responsible doing what they could with what resources they had at the time. But the special effects of 1978 were fantastic. And so began the rise of the superhero in both film and television.
Today anything and everything seems possible.