Personally I feel like Volks and Sturmpios are fine and the real weakness is the Vet 5 Veterancy.
Take the Kubelwagon for example. The Kubelwagon requires 3525 Experience to hit Vet 5 while the Universal Carrier only needs 2160 to hit Vet 3. Both units arrive at the same time and have similar costs.
Essentially this causes casualties/losses to be significantly more punishing as you need significantly more experience to reach top peak performance (maxed out Vet) vs any other allied units. While the idea of Vet 5 vet is nice and cool in practice it ends up counter productive as Company of Heroes is supposed to allow someone to come back/Catch up from a mistake and one faction is punished way more than others.
This is especially so for support weapons. The MG 34 at Vet 5 is hands the best MG in the game but at Vet 0 it is easily one of the worst. Even if you do manage to get the MG-34 Veterancy, all it takes is one lucky grenade or mortar shell and all of that hard experience is lost leaving you with overall weaker support weapons and forcing you to crutch harder on your infantry. I would gladly trade Vet 5 for Vet 3 for a less punishing Vet system.
Generally speaking XP value are in mess and need to be looked at.
So is vet bonuses.
The vet system needs an overhaul for the last 5 years.