Snafu,
The current system allows a single gunner to control all the guns that can be brought to bear on a single fighter. This is a compromise that gives a lone pilot/gunner, or a pilot with a single gunner, maximum effectiveness (without resorting to otto).
The problem arises when the buff is attacked by more than one fighter. In this case, it might be an advantage to have more than one gunner. However, it would make the "multi-gun system" that we have now very complicated.
I suppose the multi-gun system could be switched off if more than one human gunner is on the plane. Maybe we'll see that in the future. However, I doubt that there are too many instances when this would actually be an advantage.
popeye