... Vixen has the entire animal kingdom, that has ever lived on the planet, and even mythical ones, as a possibility for her power set. This includes doing things like increasing her weight, potentially morphing, shooting dragon breath, adapting gills, razor claws, etc...
Cheetah is just a woman cursed by a cat god, with super-strength and cat-powers. Yet they're able to fill up the same slot in Injustice 2.
So you're telling me it's hard to figure how Captain Marvel and Phoenix, both women who fly, shoot energy blast in various forms, and can tap into super, more powerful forms, could serve the exact same purpose in a fighting game? They're only much different in a game, because they were developed as separate roster slots.
To be honest, as cool as it is, I always thought the fact that Jean Grey (a super telekinetic / psychic power user) turned into something like Binary+Pyro (energy and flame focused) as Phoenix, was like forcing multiple characters into one. And then Dark Phoenix is basically Ryu turning into Akuma. She's like the epitome of using 1 roster slot to satisfy multiple character concepts, lol.
Comic book games are the PERFECT way to offer 1 slot with costumes and voices that serve a multitude of fans. Bishop will likely never be a full on character in a MVC game, but he, Forge, and Cable could all share the same character slot with very little modifications. Black Widow, Gamora, Lady, and Arcia from Chaos Legion could all be represented by the same moveset, with very little overall modification, if desired.
It'd really be awesome of Marvel and Capcom would embrace the old "What If?!" series into designs for these games (beyond Ultron Sigma, I guess.) Crimson Viper learned how to fit an optic blast into her moveset, I wonder what Sakura could ape from the Marvel Universe...