The difference between the O lighting it up last year and sucking this year isn't McCown/Cutler. It's the league catching up to Trestman, and him not being able to adjust. Same thing happened to Crowton in '99/2000. The BEARS would've saved a lot of money by going with McCown over Cutler. It's easy to say in hindsight that they should've gone with McCown and drafted HTJ (or whomever). But you lose any credibility if you say that the offense would still be ballin' with McCown this year.
He played great last year, and he should get credit for that. But it was an aberration. There's no way he maintains a 13 TD/1 INT pace ever again. We've seen backups come in and play well for a minute or several games, then fizzle out long term (Rob Johnson, Jeff Hostetler, Billy Volek, Charlie Whitehurst, Matt Flynn, Matt Cassel). McCown belongs in that list. He's a good guy to have on your team, like Orton. He's a career backup, nothing more.