Yes, I see what you mean. And the buildtime on M3s is remarkably fast. Thats ok though. I think its good that build times are fixed to cost at a constant rate.
What Im trying to suggest, is a lateral solution that has the same rough benefit for both factions, that does not change the stats of the units involved to a possible imbalance result, that instead "fixes" an element of what is the universal counter to light vehicles (ie: the Faust/ATNade) in that phase of the game which is a result of the interplay of what Faust/ATNade actually do to their targets.
If the light vehicles are stopped in their tracks to speed 0 by the hit, it helps offset the game internal (slightl irrational) effect of light vehicles rolling away at high speed from the point where they are hit, to where they are well beyond infantry reach.
Result? For the opponent, he can better catch up to the vehicle with his infantry to finish it off with small arms or another Faust/ATNade. I think the problem might be that even in a bumrush or M3 spam situation, it becomes even more important to maximise the cost efdiciency and expenditure of every single Faust. If the M3 can pull out, the efficiency of the Faust is basically massively wasted, as compared to if the Gren could still catch up and finish off with small arms.
This increases the relative risk for light vehicles, and makes it more important to keep range and/or somekind of blocking cover nearby to pull behind after the Faust/ATNade goes off.
TLDR: Make Faust/ATNade cause a "STOP! HAMMERTIME!" immediate halt on the light vehicle (cant speak to heavier vehicles, but I think their behavior is ok atm, due to some relation of acceleration) so that it stops dead in its tracks when hit, rather than rolling away at speed. This means infantry can catch up and continue to capitalise small arms or another Faust/ATNade on it to finish it off.
See what I mean?
Stopping won't hurt the squad inside which will just pop out and will likely win the engagement versuse ur depleted squad.I think m3 gun needs less damage,so its not as effective at killing models and even does good dmg to ACar and the faust needs to kill members inside the scout car to add a dimension of counter Mp bleed on the soviet side when using this strat and a risk-reward factor,so he can't just chareg in knowing squad will pop out with impunity after dealing dmg.
First one should ensure even with good micro its not too strong.second measure should ensure spamming it it costly.
Or other response could be lowering german t1 costs hevaily to make fast armoured car a possibility,but this would bring t2 units quite early on the battlefield which may have unforeseen effects on the meta.