I think the reason the superhero movies aren't dying is that they're actually other genres with superheroes as the characters. Per Wikipedia here are some examples: horror (Blade), thriller (Unbreakable), period drama (Captain America: The First Avenger), space opera (Guardians of the Galaxy), family film (The Incredibles), teen film (Spider-Man: Homecoming), heist film (Ant-Man), fantasy (Doctor Strange), neo-noir (The Dark Knight), political drama (Captain America: The Winter Soldier), and Western (Logan)