Tom Brady was the best QB ever, but I think he'd obviously be a net negative at safety or LB.
Come to think of it, if football remained 1-platoon, it would have hastened the athletic (largely black) QB becoming the norm. Not necessarily with Warren Moon, but Randall Cunningham (plus he punted!) and maybe a Rodney Peete would have been serviceable on D. McNair, Culpepper.....idk, imagine Montana or Marino trying to play defense, even f they grew up doing it. Once you get to Vick, he'd be a plus on both sides of the ball (I assume).
It would have been interesting.