The NFL is a passing league now. In the last 30 years just about every winning SB QB has been elite. Exceptions would include Rypien, Dilfer, Johnson, Flacco, and Foles. About 17% exception rate.
But it might be a chicken/egg argument for all we know. Are these teams winning SBs because of the QB, or does having an elite QB cause a franchise to build around him more? Does having "the guy" cause the whole team to play better? Does he become better as a player due to the team/coach?
Consider also, the list of LOSING SB teams is much more littered with one-hit wonders and journeymen. About 50%.
So you can get to the big game with a placeholder who finds lightning in a bottle for a season, but don't bet on him hoisting the Lombardi Trophy.
Just looking at the list makes me think going big on QB is a must. But almost all the big names that won did so with the team that drafted them. So trading or FA may not be as effective as drafting. If the past data means shit.