The reason I would pull Ainge wouldn't be to get a quick fix though I think it might help the season's prospects. I would only pull him if he continues to not improve. It isn't a matter of making a few mistakes. They'll all do that and you're right, the replacement might make even more. It's a matter of not continuing to make the same mistakes... which seems to be what Ainge is doing.
There is also that matter of him being very gun shy. You can't play QB in the SEC if you're afraid to take a hit. If he can't get over this, he's done playing QB anywhere.