Make it so that the helicopters after a while, have to fly back to HQ to reload ammunition. This would give players time to re-organise a counterattack and regroup. Also, it avoids pilots (specifically in the little bird and Apache) steamrolling a team and dominating the game without reloading the ammunition.

Further, make the cockpit window crack (make it harder to see) when you shoot the helicopter pilot. Since the window are not bulletproof, it makes sense that you would see damage.