Seems like PFF is all over the place. At least this guy played QB in the league.
PFF’s quarterback rankings are based on grading every player on every play and tapping into multiple years of data to project future performance. We go beyond just last season’s performances, and the grading works to isolate each quarterback’s performance from that of his supporting cast, making for more effective projections. -Bruce Gradkowski
https://www.pff.com/news/nfl-quarterback-rankings-all-32-starters-ahead-of-the-2021-nfl-season