It's a silly question, really, because without a Franchise QB even the best HC's are going to put up mediocre to pretty good numbers at best.
The real question is what the HC did with the talent when he had a Franchise QB.
Shula had ten seasons with Marino and didn't win a single SB (though he won one with Morrall). Plus, seven with Unitas, winning none.
Dungy had seven with P. Manning and won one.
Walsh, eight with Montana and won three.
Noll, 13 with Bradshaw and won four.
Landry, eight with Staubach and won two.
Lombardi, nine with Starr and won two SB's and two NFL Championships.
Johnson, five with Aikman and won three...fired in the greatest miscarriage of management until Daniel Snyder and Woody Johnson acquired franchises.
Belichick, 18 seasons with Brady as QB, won six and went to nine.
Pretty difficult not to put Belichick at the head of the HC class and Brady at the head of the QB class. It's impossible to make an argument for who was more important. They both were.
PS: Too bad that that idiot Jerry Jones cut Jimmy Johnson off at the knees. We'll never know...