A great coach can get you to a Super Bowl
A great quarterback can get you to multiple Super Bowls
Having said that, don't underestimate coaching.
Coaching - and the calls made in the 1993 NFC Championship Game - led the Cowboys to an upset win against the 49ers.
Coaching - Jimmy Johnson deducing a new play the Bills were running during practice while watching television - helped the Cowboys defeat the Bills in the Super Bowl.
Coaching - Bill Parcells' decision to milk the clock and keep the ball away from the Bills high-powered offense - helped the Giants defeat the Bills in the Super Bowl.
Coaching - Sean Payton calling an onside kick after half-time - helped the Saints beat the Colts in the Super Bowl.
Coaching - Belichick's perfect defensive game plan against the Greatest Show on Turf - led to the defeat of the St. Louis Rams.
And coaching allowed the Cowboys to squander a talented offensive line resulting in 1 playoff win and ZERO NFC Championship appearances during the Great Wall of Dallas II's reign.
It's both coaching and a great quarterback. The great quarterback simply gives the coach more to work with.