Cutler is no Manning - let's make that clear right off the bat. But Manning's struggles the last three games are illustrative of an important point.
Manning did not all of a sudden forget how to play football. What is different now is that he's getting pressured more than he ever was previously and he has no talent at wideout (sound familiar?). It doesn't matter how good a QB is, in that type of situation, he's forced to throw the ball just a mite sooner than he would have liked to, and his receivers are just a little bit less open than they would have been. In a precision league that's a dangerous combination.
Receivers don't run the right routes, and the ball gets picked; receivers are just slightly off of where they should be and the ball gets picked; or they're just more tightly covered and the QB is forced to squeeze it in dangerously, throw it somewhere else, or take a sack. Moreover, with new guys in there, QB's and receivers don't have the comfort and trust with each other to know that a guy is going to be in a particular place. This is what i think is happening to Manning.
If your receivers are wide open you would never get called a "gunslinger" - that description only comes from having to force the ball, either due to pressure or no open guys. It's why I think you can't blame Cutler all that much for his struggles as a Bear. The pressure from an totally incompetent O-line (which still stinks, btw - just not quite as badly) has been well-documented, but the lack of any very good receivers is just as much a part of the problem. No big targets to make up for lack of separation, no great route runners to get open (how often has a bears player really gotten truly wide open? not often). As good as Bennet has been recently, he's still not a true number one receiver - but i think a lot of his success comes from Cutler's familiarity with him - they know each others' games and are on the same page.
For all of Knox's big play success, it never feels like he and Cutler are on the same page, and there have been many examples of him running the wrong routes, or failing to follow through on a route, causing a pick.
It's not just that i think Cutler would be a better QB with a decent line and good receivers, I think he would be a different QB. We've never heard "gunslinger" thrown around regarding Peyton Manning - but if he had the talent he has now for his whole career I bet we would have.