What people don't understand about Cutler is that he was a quarterback under development when he came to Chicago. His second year as a starter in Denver, when he went to the probowl, he was a markedly different quarterback from his first year in Denver.
During each offseason he watched film with Jeremy Bates on the pocket presence and footwork of Manning and Brady because his feet weren't active enough in the pocket so sometimes when he wanted to get a ball out quickly he wasn't going through the whole motion but throwing off the back foot. He also adjusted his throwing motion because he used to hold the ball too low to the chest on dropbacks, which would cause him to overcompensate on the throwing motion and have the ball sail high on him. He also had a tendency to telegraph his throws because he wouldn't position his shoulders perpendicular to the line of scrimmage and his body lean allowed defenders guess where he went with the ball. He fixed a lot of these things year over year in Denver, but when he came to Chicago i saw him regress to his rookie year mistakes, I don't think that's just O-line, i think that's environment and coaching, could Chicago have provided both talent and coaching under the Angelo regime? I doubt it...
I know in Denver Cutler was close to his QB coach and respected Shanahan very much, basically when McDaniels went to the Broncos, Cutler and Marshall both thought of him as an inferior coach and scoffed at him during the interview/screening process. Their first meeting was filled with animosity, it was all over the media there, from the very beginning they disrespected their coach and McDaniels would eventually trade both of them (putting cutler on the market for Matt Cassel), and the rest is history.
Now in Chicago, the offensive staff, the linemen, the receivers were all really bad, not below average, but bottom 5 in the league. I don't think I've seen a worse set of starting wide receivers in the NFL (for a whole season) than what the bears had out there in Hester and Knox, and what's worst is that I'd say our O-line was even worse (pass protection wise). But probably most importantly, the offensive staff here was always in flux, different guys every year, none of them were particular great, and that's why Cutler kept lobbying for QB coach Jeremy Bates, it was the only guy he felt he could trust to improve him as a QB.
You can tell Cutler trusts Trestman, just look at his demeanor in Offseason, even before the first preseason game, with no idea of how good his O-line was, Cutler looked different, he looked happy. He looked happy because he trust that his coaches have him in the right direction. His mechanics are back on track, he's not reverting to the same mistakes I saw him make in his rookie year. People forget, in Denver Marshall was the trouble maker who had a bad attitude, and Cutler was always revered as a great team leader who kept Marshall on track. Somehow after the trade a whole lot of stuff about demeanor got drummed up mainly due to the fact that Cutler more or less flipped off McDaniels, it says a lot that all his teammates sided with Cutler. Marshall, Scheffler (his tight end), Ryan Harris (his right tackle) and Peyton Hillis all sided with Cutler and had shitty relationships with McDaniels after the Cutler Debacle, as a result they all got traded.
I'm trying to say the kid didn't just need talent around him, he needed some form of mentorship because his organization got blown up abruptly in the middle of his development. Its a combination of a good line and good coaching, every top player needs coaching to remind them of what they are doing wrong, especially if they are young. When Rodgers came out for his first start, he was on a team with leftovers from Holmgrem's legacy and the Walsh era, and had 3 years on the bench to watch and learn from Bret Farve. Guys who sit behind Bret Farve seem to learn a lot, I heard this other guy Kurt Warner turned out pretty well too.
Football is like everything else in life, you need good guidance and mentorship to learn, Cutler lost his when he was traded out of Denver, it's actually beyond just the O-line when the QB is so young. Now if you're buying Peyton Manning from Free Agency, yeah, maybe your coaches don't matter, but if you are trading for the youngest Pro Bowl QB in the league, yeah your coaches and environment is going to matter a lot.
In this case the Bears didn't really provide that guidance, which I think was more critical than even the O-line or Receivers. Cutler should've taken another big step forward in mechanics from his second to his third full season as a starter, but somehow he regressed.
That's the biggest mistake for the Bears, but now we have a chance with Trestman. Cutler clearly trusts this guy.