This is the problem you have when units resolve damage differently.
And the dice is used in a deterministic way.
There is no fine adjustment avaible to help the balance , and subjective PV allocation based on limited playtesting and biased views.Means that subjective arguments are all that is avaiable.
Is Rock overpowered?
Paper doesnt think so, but Scissors wants it nurfing now!
The current vehicle damage system is the best comprimise available with the current direction of the rules.
However, it is far from the best avaiable solution.
In the same way 5th ed 40k is the 'best' encarnation of 40k current rule set.(3rd ed onwards.)
But in comparison to other modern rule sets written focusing game play, it is very poor.(In reguards to clarity and brevity.)