I don't buy that argument for a second. I'd reference you back to the JLA from the comic book (most recent series) placing Connor "Green Arrow" Hawke on the team. Compaired to Superman, Wonder Woman, Green Lantern, Martian Manhunter and Flash, this guy is incredibly outclassed in raw power and Batman would slap him around like a green shirted step child. Just because you can't hang with the big dogs in raw powers doesn't mean you are worthless. Connor essentially saved the whole league just by being in the right place at the right time and using one of his pops old boxing glove arrows to save the day.
Any GM worth his salt should be able to have something for anybody in the team to do regardless of power level. Having the big bad in the campaign constanly grabbing for the most vulnerable team members, although it would make real world sense, goes against genre staples.