Problem is Volks are way too versatile. Schreked and at vet 3+ and in blobs they can melt infantry and armour really quickly and require almost no skill at all to use.
A-move OP, Relic nerf.
But seriously they should have had AT infantry as completely separate squads of 3 or 4, very poor AI to the point of being defenseless if not protected with dedicated AI infantry. That would sort of help the Volks blob problem because a) it'd be harder to vet up AT squads and b) you can focus fire depending on what you need to kill.
As it stands vetted schrek volks blobs have schreks evenly distributed between them so that even focus firing isn't that effective.
Making a Tier 2 (meaning ISG tier for me) unit like "tank hunters", that come equipped with 2 shrecks by default, having verry poor AI capabilities while costing an appropriate amount of manpower would be the only choice if we consider removing shrecks from volks and give them other upgrade.
Early-middle game anti vehicle counter for OKW will translate into raketen+Puma combo (if OKW player starts with T3 building) or into raketen+tank hunters combo (if OKW player starts with T2 building).
That would be probably an interesting way to change OKW, but I sincerely doubt we will see that in the official game. Maybe in a mode.