Both Fantasy RPGs and Supers RPGs have assumed settings. For Fantasy you’re looking at a world with Humans, Elves, and Dwarves. There are dungeons filled with evil humanoids, dragons, demons, and undead. And all of it takes place in a world where knights on horseback live in castles and wizards can cast spells to devastating effect.
The assumed setting for a Superhero game is quite different. They take place in a city of some sort, a massive urban sprawl that may or may not be New York but probably looks quite a lot like it if you squint. Heroes come from all sorts of backgrounds. Mutants, magical beings, lab accidents, and human looking aliens all fit nicely, each with their own reasons for fighting the criminal thugs, giant robots, and crazy ape men who are looking for world domination. Pastiches of current comic book characters are common and even expected.
Damn. I just want to throw these two worlds together and see what pops out.