Well obviously if you place it too far forward it can be easily removed but it becomes far to powerful when placed a bit farther back and even zooks(which would cost a lot of munitions to get enough to kill a Schwerer) in smoke can be burned out with flame grenades and explosives and su 76s can be countered by a single at gun.
Yeah, this is kind of the essence of the game. One unit destroys another, so you need a third unit to stop the first from destroying it.