Why not have both work on it? Carter may produce some stinkers but he also makes some great episodes, too.
In the mid-nineties, sure.
Not that I would want Vince Gilligan to become showrunner. His talent would be wasted attempting to fix what can't be fixed. Let the mythology arc be the comically convoluted mess that it is, and let writers like Gilligan take care of the standalone episodes.
edit: Actually, I have to admit I really liked the season 8 premiere so the last time Carter shined is not
that far back in time. The last time he was consistent however was the mid-nineties.