I think it's sort of a fair balance seeing as how almost all planes with F3 mode have a gunner. Only exception is the Bf110, Mossie, and recently added IL2. Think of F3 mode as a way to balance the fact that you had 2 an extra pair of eyes in the plane.
IMO, if the above three planes got F3 mode, it wouldn't be THAT game breaking. It still performs the same. Cockpit view in the 110 is excellent, Mossie is decent but not great, and the Il2 is horrible, but the Il2 and Bf110 both have gunners.
So I say let all planes with 2 or more persons in it have F3 mode.