I think vehicle crits should only have a chance to occur when you make the "killshot" on a tank but damage has almost no overkill, lets say tank has 20 health left and the shot has 25 damage and thus the tank ends up with -5 health which could translate instead to a possible critical hit. If instead the tank has 20 health left and final shot does 120 damage meaning the tank ends up with -100 health and that means it will always gets destroyed with ZERO chance of critical hit because the overkill is much greater.
I think this would still keep the immersion but still get more power to the player to influence the RNG factor. Win win situation.
Myself i think fixing unit hugging when a squad is moving which results in mine squad wipe or tank shot squad wipes is more frustrating and more important to fix than crits or planecrashes.
