Look at coaches in recent memory that had a QB, then didn't. And were considered good coaches, then weren't. There are TWO in our division. Carroll was 7-9 two years in a row, Wilson arrives and BAM he's winning left and right. The Cardinals get Palmer and they go from losing to wining. Palmer not playing or not playing well? Well the Cardinals lose most of those games.
What's the difference in Carolina this year?
How relevant were the Saints before Brees arrived?
Lions? Perennial losers until they drafted Stafford.
The list goes on too..........
It's not ALL the QB of course, there are plenty of other factors, but that's the big one.
Head coaches matter, but not as much as the QB/Owner/GM.