So the other 12 would be mediocre as well?

Look, Favre's got that nutty smell of fresh from the toaster whole grain goodness about him this year, but last year he was solid.
He had gaudy numbers but the numbers and the wins were because of things going on elsewhere in the team. Bleacher Report did
their top QBs this last off-season. They put Favre #5 on their list based on his year in 2009. But realistically, I think pretty much all the guys down to Cutler at 15 (14 if you take out Favre himself) could have had the same type of year Favre did last year if they had played for the Vikings. And if you're in the #13 - #15 range in a 32-man league, you are pretty much the definition of mediocre. As I said, mediocre can be good. Half the teams don't even have that much.But noone should be pretending that Favre was the #1, or even #2, reason that the Vikings were 12-4 and in the NFC Championship last year.
I have no idea where you're going with this. Favre is the only reason they were 12-4 and in the Championship game last year. They're a wildcard team with Peterson running and Jackson behind center. So it's not Peterson. It's certainly not the coaching. What's so great about the Vikings that so many QBs could have had that type of year? Do you remember how amazing that year was?
They would not have been 12-4 last year with Peterson running and Jackson QB'ing. I agree.
But Tavaris is not even a mediocre NFL quarterback. Tavaris is, in what he has shown, a bad NFL quarterback. If you had put a legitimately good NFL quarterback with the Vikings last year: Brees, Manning, Brady, I think they win the Super Bowl.In addition to Peterson, they had a good defense, a decent offensive line, a good tight end, and a wide receiver who had a break-out season. Other than Peterson, they weren't necessary elite anywhere (except defense arguably) but they were a team that also didn't have any holes. There was nowhere to exploit them. Those are the reasons they were in the NFC championship. Favre just had to be good enough not to screw it up. And he was. And since teams overplayed the run the first 10 or 11 games he looked a whole lot better than that.
And in retrospect, the idea that Favre was a mediocre quarterback last year who got a year older, lost some protection up front, and no longer can exploit teams overplaying the run fits the story of 2009 and 2010 a whole lot better than the idea that Favre was an elite quarterback last year who turned into dog-crap this past off-season.