He won the AFC championship game without Brady against the Steelers to get to his first Super Bowl. On the road. Brady goes down in game 1 of 2008 and hurt the entire season. He wins 10 or 11 games with Cassel. Meanwhile in Dallas, we win 4 games when our QB goes down in the middle of the season.
To discount a coach who has built what he has is flat out silly. Look at every single great coach. Now name me one who didn't have a great QB. On the flip side, name me a great QB who had a terrible head coach and lets compare accomplishments. Head coach and QB go hand in hand. They are the 2 most important aspects of a team. If you have one and not the other, you aren't going to be as successful and really not even close.