I don't know this, but I doubt that PFF ranking is based on the points scored metric. Points scored is partly a function of the D, including literally points scored off turnovers but also the net effect of field position provided by a good D. It even takes special teams into account. I don't think that is the metric used by PFF here.
Of those four, Vick is apparently not playing because the Jets are intent on playing one of the worst Qb's in the league last year. Amaro has been having a poor camp, and btw I see that Cumberland is banged up. I do think CJ will help, especially catching passes. But the Jet running game last year was ranked sixth, so how much better Johnson will make the O is not clear. He will probably take more touches away from Powell than Ivory, but Powell had some decent stats. Decker is a clear upgrade, though.
So say you assign a baseline of 500 for every team and then you look at the average stats for each position and add or subtract points based on how they played per game and adjust for statistic improvements over the course of the season. It still doesn't really work because rookies in this instance are being judged off their NFL career, one preseason game?
I think people rely too much on blind stats, I worry more about how #s were accumulated than the actual #s themselves.
Id guess it wasnt the main focus for them. They probably have a system. But in the end these rankings are all pretty insane if they dont explain their formula. Is it points, is it yards, is it something else? No one really knows.
Not saying I agree with the ranking but you have to consider other teams' roster moves as well not just ours.