That's all very true but I feel like you are downplaying the QB spot. You did pick some extremely average (and LUCKY!) Qb's to make your case. And I apologize, I do not have anything as specific as you to counter...
Those average, and lucky, quarterbacks are what makes the case. If we're going to say essentially you can't hide the quarterback, then there can't be any cases where the QB wasn't at the center of the success. However, there are cases throughout NFL history where these average NFL starters got Super Bowl victories because of the team they were on. There are also cases where these great NFL starters got Super Bowl victories because of the teams they were on.
How many rings would Aikman have now if he had been on a team that didn't have the No. 1 defense, that didn't have the NFL's rushing leader, that didn't have the right head coach at the right time? Those elements, aspects of the game, keep it from being all about the quarterback and allow the QB to just play his part and not have to be relied on to be the savior of the team throughout the postseason. Again, sometimes that part is bigger and sometimes it is smaller.
Although I used Eli as an example earlier, throughout New York's postseason runs in 2007 and 2011, Eli did make plays to help his team win. However, if the defense had not played as well as it had, then those plays would have gotten overshadowed, especially in the two games where his numbers were not great, by the plays he did not make. The narrative would have been that Eli wasn't good enough, which he wasn't without the defensive effort. Just like Romo wasn't good enough in 2014 against Green Bay because of the defensive effort, because of Murray's fumble, because of Dez's drop, etc.