Seems that would only apply if you're talking about a single round hortlund. If its penetrating enough to put a visible opening in the armor... and you have 6 .50's shooting at close to the same area... well... I think even you can understand that it will be a cumulative effect.
Some months ago, I watched a program on the Discovery Channel about the P-47; there was one gun camera film they showed of a P-47 on a ground-attack sweep mission strafing a truck somewhere in France. When the pilot opened up on the truck -- at a range that was described as being about 400 yards -- the dust puffs on the ground from the bullet impacts covered an area four times the length of the truck in each direction when the pilot opened fire, shrinking to about three times the length of the truck when the pilot ceased firing and pulled up at about 200 yards range.
It seems to me that the problem with machine guns against tanks may not be that 80 rounds of .50 fire won't achieve enough damage against the deck and turret top armor to knock out the tank, but that the way that the
shooting platform is modelled, each barrel is rigidly clamped into the airframe, which is rigidly clamped onto its line of flight, so that if the plane's guns are calibrated for 400 yards, at 400 yards all of the bullets in a one-second burst are going to hit the exact same spot on the target -- recoil torque and barrel flex being completely omitted from the ballistic calculations due to the increase in compute power required.