great season vs his bad ones is consistent play by a good QB. He fits the same profile as Lavell and Bronco in that regard. You have a really good QB, you win a lot of games and have great seasons even when the D isn't so good.
You don't have a great (healthy, or experienced) QB, you lose more often.
To Bronco's credit, he has done better with a lack of talent/health/experience at QB than Crowton.