Teams do stack the box against teams that have "good" running backs. You're delusional if you think they don't. Do you even watch football? I guarantee that you don't from that retarded question.
No correlation? Says who? YOU?! Again, it's absolutely moronic to think otherwise. It's simple really. Our offense is mainly quick hitters, couple of longer passes to Ebron/Tate/Jones and our running game consosts of short dumpoffs to Riddick/Zenner in the flats or over the middle. THAT'S our running game! We don't even have Abdullah to have somewhat of a threat to run the ball.
You don't think teams stack the box against Peterson? Why is Gurley struggling in LA and guys like Britt and Quick are having success in the passing game? Newsflash, genius! Box is stacked!
Lets look at the Top rated QBs this year, based on QB rating, and the running game YPC for those teams:
Brady (3.5 YPC since Brady started, 29th in the league)
Ryan (4.4 YPC, 9th)
Brees (3.6 YPC, 28th)
Stafford (3.9 YPC, 21st)
Carr (4.8 YPC, 6th)
So 6th, 9th, 21st, 28th, 29th
Lets look at the top 5 from 2015 and where their running game finished
1) 7th
2) 23rd
3) 12th
4) 29th
5) 30th
Yet again, Top QBs had statistically a worse than average running game overall.
Facing 8 in the box. Now this is a little harder to find. Considering we are typically two+ WR sets. I looked at those stats. Most recent was a few years back. Average was 12.6% there was 8 or more in the box. Lions were 14%. Buffalo led the league at 23%. So Lions faced 8+ in the box slightly higher amount.
Basic football should tell you, the more WRs you put out, the less that will be in the box. if you run a two TE set, with a FB and HB, you are going to face 8 in the box often.
You're taking a few execptions and pretending it's the norm. Peterson did face 8 in the box more. Peterson also had a FB in front of him more.
Based on our sets, we face 8 in the box no more or less than most teams.
Stafford doesn't have it "harder" than any other QB because of the defenses he faces.
There is no indication good running game is a prerequisite to a good passing game. In fact the opposite is almost true, the better your QB and your passing game is there is a strong possibility your run game is less effective.