To me there is a bit more to the dominant quarterback than just physical skills. Namath, Stabler, Barker all had great stats in their careers, but they also had that special something that inspired their teammates. Their leadership skills were such that they always thought they would find a way to win. Mike Shula was dominant in that respect, even though his physical skills weren't close to Namath's or Stabler's. Greg MacElroy had great leadership skills, even though he didn't have great legs or a great arm.