I'm sorry but Kevin Vickerson and Justin Bannan are nowhere near as talented as Soliai and Starks (two Pro Bowlers). The point I'm trying to make is that PFF is no better judge of a player's value than the stats I'm looking at.
They don't have to be as talented individually to be as good or better a unit.
Let me say it again, Denver was 3rd in rushing yards allowed and it is no coincidence that PFF had them rated as the 3rd most effective defense stopping the run.
It looks to me like PFF is taking their own grading system and creating a similar thing to QBR for each position.
PFF takes it a step further.
The view film (WHAT A CONCEPT) of every snap a player takes and decide if that player was effective on each play.
So if Dumervil took 60 snaps in a game and 30 of those snaps were against the run, they look at whether the offensive lineman was able to block Dumervil, move him off the line etc and that is how they determine how effective he is against the run.
Rather than looking at raw data (stats), like how many tackles a guy got. They look to see if the player was effective on the play.
Example - on a running play, Dumervil sheds his block and makes the running back cut the run back inside. The middle linebacker then stops the running back for a loss.
Dumervil doesn't get a tackle or a stop on the play. But he gets a positive grade because he did his job.
That's how PFF grades. It is better than anything else out there. There is a reason so many sports writers, radio hosts and even NFL teams regard PFF so highly.
So my advice to you would be to learn more about something before criticizing it.
1) Why do we grade?http://www.profootballfocus.com/about/grading/
The goal of our detailed grading process is to gauge how players execute their roles over the course of a game by looking at the performance of each individual on each play. We look beyond the stat sheet at game footage to try to gain an understanding of how well a lineman is blocking on a given play, how much space and help a runner is being given on a play, how effectively a pass rusher brings pressure or how well a defender covers a receiver.
We collect lots of extra statistics such as yards after catch, yards after contact, missed tackles, dropped passes etc., but our real focus is on grading individual performance on each play. Did an offensive lineman seal his block to spring the runner through a hole? Did a defensive lineman beat his block to force a runner to change the play direction in the backfield? Was the crucial third-down completion due to the quarterback beating the coverage or a breakdown in coverage?
We examine not just the statistical result of a play, but the context of that statistic. The defensive tackle may have made a tackle on a play, but if it was 3rd-and-5 and he got blown 4 yards off of the ball to make the tackle after a 6-yard gain, that’s not a good play.