But that's not balance. There shouldn't be more than a 10AC spread between the average melee (excluding raged barbs) and the high AC build. That way monsters can be balanced so that the high AC build only gets hit on a 20, and the average gets hit half the time. Sucky AC builds continue to get hit all the time.
The current range is so great that you either have a "gets hit on a 1" or "gets hit on a 20" build, there is very little in between.