Congratulations, you've proven that Matt Cassel is a better quarterback than Curtis Painter. Confirmed by the fact that Cassel led the KC Chiefs into the playoffs a couple years after his stint in NE while Painter is flipping burgers or selling insurance or something.
I'm not going to pretend that Matt Cassell is some sort of stud, but he was good enough that a good team could work with him, he was a smart, reasonably accurate thrower and he grew a lot that year. he reminded me a lot of the guy Tom Brady was in his own first few campaigns, and while obviously Cassel didn't have the upside to become what Bray has matured into, he proved he could lead his team well enough to beat good teams.
Painter by contrast was a disaster, learned nothing, and led a solid team deep into the cellar. The contrast goes to prove that we could have done so much worse when Brady went down that one year. Heck, if I recall correctly there were people that year who WANTED us to. Fortunately the Patriots felt they had enough talent to win and they were right. They came within a 4 way tiebreaker of the playoffs if I recall correctly.
Not sure the Colts were similarly committed, since they basically tanked to get a high pick that year. Their commitment to tanking is as obvious as the fact that they kept Painter all year. No way BB does that. Cassel deserved and got his chance, but if Cassel had been that horrendous, he would have gone to the next guy. Painter was the player the Colts threw out there in order to have a warm body in the position while they tanked. If I recall Carson Palmer was on the move that year, and if they weren't tanking for Luck, he would have been a Colt. I'm fairly confident that that's the move BB would have made under the same circumstances.