Sakai, the pintle gun is only disabled if the turret itself is disabled. It isn't a separate system, and no amount of mg or cannon fire will kill it, until the turret receives enough damage to "break".
And we're not talking about diving lancs, or strafing a plane hovering at 100' until it pops. The point is that the pintle doesn't die. A short burst from the pintle can and does injure the attacking pilot, or damage the radiator or oil systems. A long burst from the fighter does nothing to the pintle. If my Il-2 is incredibly vulnerable to light mg fire, how come the soft unprotected target isn't?