But if the numbers being better than Jameis is grounds for keeping him vs Jameis, shouldn't the same be applicable for keeping him over Carr who also had a worse QBR?
No. Because Carr wasn’t in our building running our offense.
The whole idea here is that you have a QB who ran a version of our offense very well. Then a new coach came in and his skills didn’t mesh with the new coach and system.
Edit; QBR is also a different stat entirely. And even in those PFF grades, no one was objectively trying to argue they proved Dalton was on the same level as some of the players close to him in those rankings like Mahomes, Allen, etc.