With my experience in Marvel Universe roleplays, nobody ever wants to play the humans. Everyone seems obsessed with creating powerhouse mutants/aliens/superhumans/asgardians etc with overly convoluted histories. I want everyone to keep in mind that not even S.H.I.E.L.D. has a clue as to how many mutants or superhumans there are or what they're capable of. I want there to actually be more humans in the team than others. So, yes. If one of your characters is inhuman, you'd have to create a human character as well.