You really think that if a 3,000 lb airplane runs into the top turret at 300 mph that NOTHING is going to be bent, broken, strained, wrenched, torqued, twisted, mangled out of position, etc? If that turret turns at all I bet it is never as smooth or quick as it was before the impact.
For one thing if it happened for real the tank would probably end up laying on its side.
Yes tanks should roll over bushes, small trees, lightly built buildings, etc without takeing damage. That far I'll agree with you.
As for taking damage from a low flying plane, roll the dice 1 - 4 gets off no damage, 1 - 4 takes fatal damage, and a couple of light to moderate damage in the middle which are fixable with supplys.