And the part where Mactavish destroys a helo with a SMG is like.. I dunno. Just doesn't make sense.
I don't think you understand how powerful guns are.
In Vietnam, the Vietcong shot down helicopters with AK-47's. Those rifle rounds turned the originally bulletproof windshield into swiss cheese. Plus, if you shoot the rotor of a helicopter, the entire thing will crash. The rotors are essentially the weak points of all helicopters. The only helicopters meant to stand up to gunfire are gunships, but you were fighting scout aircraft with little to no armor plating. It's entirely realistic, actually.
In my game Price shot the gas tank with his rifle, Felt so much more awesome.
He shot the rear rotor, not the gas tank.