Actually, the DC world is a lot more human than a lot of people realize. Especially if you take in the Batman series or any of the parts that shoot off from that. Nightwing, Robin, Hungtress, Batgirl, Catwoman...all normal everyday people, as well as Green Arrow. Black Canary had powers, the power of voice to blow down walls, but in the end it came down to her martial arts for how good of a heroine she is. The power levels are actually about even in both universes, I'd wager that Marvel is the more powerful of the two but that's probably because I don't read much marvel. =OP
Point being okay, yes there should be some kind of power cap, so you don't have a person that blinks and can destroy a planet. BUT, it shouldn't limit players to creating only people slightly stronger than humans. Then you wouldn't have hardly anyone from the Marvel directory to play. Spiderman is class 40, for example, meaning he can lift 40 tons...not exactly your everyday human.
I basically think if you're going to have this super powered human, you'd better make them with a superpowered weakness. I like Superman in this sense, because while he seems invulnerable (at least in the animated version) he's susceptible to getting taken out by vast amounts of electricity, kryptonite, and lets not forget his biggest rival is Lex Luthor...and ordinary man. ^^