After I made my post, I anticipated someone making that counter-argument, but admittedly you went into much more detail than I was prepared for lol. Nice job!
The thing with great QBs is that in all instances I can think of, they had solid running games and solid defenses. The times when they didnt - 80s broncos, 90s bills, last Pats SB, etc - the team lost. Elway didn't win until he had a top ranked defense and Terrell Davis. The only time the Bills competed was the year their defense was strongest. Peyton Manning always had a running game, but it wasn't until Dungy got the defense playing well that he won his. In short, there are plenty of examples of teams with great QBs who won SBs WITH solid defenses, but not many were the great QB won w/out it. I guess what I'm saying is that the common denominator among SB champs - in my opinion - is the strong defense...not the great QB.