One of the biggest flaws I see on the Offensive side of the ball
Sacks are a "QB Stat" Not necessarily by PFF standards but by coaching standards, you've never heard this? its true, there's no way to measure if a Qb is holding onto the ball too long per play. (theres a measurement of release time, but its too general) Or if the Qb couldve just known when the play was over and threw it away. A ton of young QB's don't know when a play is over, and they'll take a sack or force a pick etc. You can never sack a QB that throws it away or throws a complete pass.
In response to the edit. I think all that shows is that some sacks are the fault of the QB and others aren't. So I think if you want to have a QB stat for sacks, you need to look at each sack individually and decide if it was the fault of the QB or something else. Otherwise, I don't think treating sacks as a QB stat is really a useful analytical tool. Put another way, not getting sacked a lot doesn't make you a good QB, but it is true that lots of good QBs don't get sacked a lot. But, I don't think the stat itself tells the full story.
There are times that a QB gets hit from the blind side where he can't get rid of the ball. And there are times when a QB should move up in the pocket or roll out to make a play to avoid a sack instead of just throwing it away. Sometimes that move ends up in a sack, but I think you would rather that than a guy just throwing it away every time he feels pressure.
So while sure some sacks are the fault of the QB, not all of them are because as I said some are caused by scheme, play call, play design, missed assignment, OL getting beat, etc. and can not be avoided. It's why we now have advanced stats on how long a QB holds the ball and how much time he has to throw. It's because not all sacks are equal and not all sacks are solely the fault of the QB which is why I don't think it's right to call it a QB stat. And on the other side, a lack of sacks isn't necessarily because the QB is good. It could be that you just run the ball a lot, use a lot of quick passes, you have a great OL, or the QB is throwing the ball away too early.
And FWIW, some people also think wins and losses are QB stats to and I disagree with that for similar reasons.