the myth that running the ball well makes you win
No you don't HAVE to do it well to win. It does help though, and just looking at each superbowl winner's statistical ranking as proof that you can't win that way (which I don't think you're implying, but could come off that way). Assuming that a few plays break either way, the headline writers would say that the ground game dominance helped the 49ers win the game. The same way they did for the Niners-Packers game two weeks ago.