I haven't watched every Vikings game, but it all boils down to this for me. IF Bradford can be under some pressure and toss pinpoint perfect passes 10-15 times a game for bigger plays, their defense can get a couple takeaways and their special teams are good, they'll still win games. Won't matter who's calling plays.
The hard part is, it's not hard to do that for a game or 2. It's hard to stay that accurate when you're offensive line is that bad and you're getting beat up pretty much every single down. If your defense isn't covering for an inept offense and giving it 2,3,4 extra possessions a game on a short field, it's harder to win. If their line doesn't improve, I don't card who is calling the plays, Bradford won't be able to hold up his end of the bargain. Maybe they get a shortlived blip in production because some tendencies changed, but new ones will be found and figured out in a couple weeks. There's only so much you can do behind an oline like that with limited playmakers and an immobile QB.
It's still going to take perfect defensive play and good special teams play to cover up for this offense