Superhero movies can be anything from Deadpool to Guardians to Watchmen to The Dark Knight, some people will like 'em more on the one end of that spectrum or the other, and some will like all kinds, but to say that all should be one way and that that's the only correct way to make them is rather limiting.
I especially don't get this knee jerk reaction of everything must be "fun"!!! whenever anyone suggests they like something different, because if anything the "fun" superhero movies are in no danger of disappearing from cinemas, they're the easiest sell to mass audiences and there's half a dozen scheduled every year for the foreseeable future. They're not going anywhere, so hide your pitchforks every time someone mentions they'd also like to see something more on the serious side...