That and being one of the best clearance winners in the game from day 1. It's really really really revisionist to ignore that IMO. You are right though, his running was a real weakness when he started, and his kicking wasn't great, he improved both of those things a lot. Without that drive he probably ends up more in the Sewell or Cunnington (dare I say Tom Mitchell) type, good at the clearance and not much else.
I just don't think Mitchell is a good comparison at all. Mitchell was always GREAT at one thing but he had big flaws too. Mutch does everything OK without being standout at anything.