The thing with Cutler in Denver is that virtually everyone who played for Mike Shanahan had their best QB years ever, Jake, RG3, Griese etc. the one guy who arguably didn't was Cutler and that's because he was a rookie when he got there. Shanahan is brilliant at crafting a system to hide the weaknesses of his Qb. the problem is eventually he assumed the QB will get better to where he can open up the full playbook, Jake never did so he replaced him with Cutler, and then they fired Shanahan and traded Cutler because the new coach McDaniel wanted his own guy.
Arians IMO is NOTHING like Shanahan, he has his system he wants a QB to fit it, not the other way around.
Excellent point Russ, Arians needs/wants a QB that will fit his system and he doesn't/will not/won't modify his system to fit a QB that although may be a good QB just isn't a good fit for the Arians system. The problem with system coaches is it's brilliant when all the parts are in good working order and running smoothly, however when one of the parts breaks down, the whole system comes to a grinding halt.