Needless to say I disagree with your assessment of PFF... Tell me where and how I'm wrong.
Thanks for the detailed reply and in return here's a long post that I wouldn't blame you for not reading. The TL;dr is I don't think you're wrong, I just think by getting caught up in the details you're not seeing the forest for the trees, which is the trap PFF likes to pull to sell their product.
You can read their methodology, they post it:
https://www.profootballfocus.com/about/grading/ . Maybe that convinces some people, but to me it just reads like a snake oil salesman drooling over all the easy money. They even give a couple actual accuracy numbers to make us feel warm & fuzzy, like "we’re confident that our work is very close to 100% by mid-week (actually stands at 99.98%)".
Problem is, that number only applies to their "player participation" data. "As for the grading ... we feel as strongly about the accuracy of the grades."
Oh, ok, well if they "feel strongly", I guess the grading is fine? Why don't they just say their grading is 99.98% accurate, too? Because they don't want to lie. Grading is always subjective, you can't call it any percent of accurate. So they explain, explain, explain this "scientific, foolproof, so-many-pairs-of-eyes-it-can't-fail method" for everyone to trust (and pay them for).
Hey, I take my hat off to them. It's a few guys from the UK that never played football that are now rich off it. I should do the same thing and sell the English Premier League a bunch of my stats that me and my dog watched (four pairs of eyes) -- and I've actually played soccer, er football!
But instead of bogging down into the minutia of their process, the bottom line is no system can do what people want from PFF.
Just an easy example, look at the safety grades posted above. Antoine Bethea is ranked as the #6 top coverage safety in the NFL. But here's what PFF said about Bethea last year: "Where Bethea struggles is in coverage, particularly on the deep ball ... his -4.9 grade in coverage was 17th-worst among safeties ... Now on the wrong side of 30, it’s reasonable to think that his coverage protection will only decline from here."
So Bethea puts on the SF jersey, drinks from the fountain of middle age, and poof! magically went from not being able to cover a wet paper bag to one of the best in the NFL?
Now, note he replaced Donte Whitner in 2013, who "had the fifth-best +10.5 rating in coverage". So let's see, the SF safety was 5th best.. they replaced him with the 17th-worst.. and now he's 6th best.
In hindsight, maybe this makes sense? Maybe the SF defense scheme makes the safety position shine so makes Bethea look great now? Maybe if PFF reported their grades as simply nameless positions like "SF safety position coverage grade is 8.4" that would make more sense. Maybe if they applied a team/scheme discount to each player it would make sense? But what about the fact Eric Reid sucks ballz now, so maybe it's not just the team making safeties look good. And at some point, don't the players make the team?
When SF idiots were crying at the time "SF can't lose Whitner, he's 5th best according to PFF!" and "SF safety is going to suck now because PFF graded Bethea 17th-worst", that was wrong. The PFF grades overrated Whitner and were screwing Bethea.
Perhaps the blame should be put on the media and those that derive the wrong conclusions from the stats, not PFF.
But then the question is, what is the "right" use of the PFF grades that shouldn't get any blame?
Pretty much any way anybody uses the PFF grade -- whether to state a guy is good, sucks, average, whatever -- is so subjective that it is basically worthless. The real success of PFF is it doesn't say anything new. If a guy is good, anybody watching the NFL already knows. But they scurry over to PFF and see it backed a number, and it makes them feel like a big expert to announce it to the world "hey I think so-and-so is the best, and just look at his PFF grade that proves I'm right!"
PFF just makes money off reassuring someone's opinion with the facade of "legitimacy". And next year, when the grade is reversed and it was so obviously wrong in hindsight, nobody remembers to mention it.