12 of those top 20 players are still active, and another 4 of them stopped playing 3 years ago or less.
That suggests QBs haven’t gotten better, it’s just gotten easier to put up big numbers.
Matt Schaub isn’t better than Roger Staubauch.
Derek Carr isn’t better than Johnny Unitas.
Andy Dalton isn’t better than Dan Marino.
The passer rating may be fine for comparing contemporary QBs, but it’s worthless for comparisons across time.
It says more about how the game has changed than it does about a QB’s abilities.