Volks being the only OKW unit to actually ever reliably vet up is stupid and a problem not with Volks but the insane way the veterancy system works and the cost of OKW's units.
Volks are cheap infantry that vet up due to the fact they shoot at expensive things, the Stuka and Sturmtiger vet up slow as garden due to the fact they are very high fuel cost units shooting at only MP costing units (and the fact they don't do much damage killing infantry as they do hitting tanks).
Volks veterancy bonus's make them better against infantry by design, as Volks are garbage against enemy infantry till they receive vet. From a design standpoint the challenge is making Volk's scale more naturally with out making them even worse off when facing enemy infantry or more OP versus tanks.
I brought up my Sturmtiger use as a point that I don't enjoy the stale meta any more than the average person does which Is why I like to use rarely utilized units.
Exactly, so fix Volks by removing the shreck or making the unit become a tank hunter unit when they buy one, which could give them 2 shrecks for a higher amount but reduce severely their veterancy gains. The issue with the CoH2 engine is that units vet is balanced around either AI or AT... AI units tend to have lower Vet thresholds since what they are killing are worth less XP, whereas AT units threshold will be higher due to as you say the 'more expensive' units they shoot at.
CoH2 engine can't differentiate between the two, I.E a unit which is designed primarily for an AI role will vet extremely fast shooting at tanks.
The Volks vetting can't be fixed unless their design is changed, and lets be honest the current volks spam into vet5 shreck blob is boring... Making changes to their design and buffing their other counters (raketenwerfer) which in turn means if a US/Soviet player goes for a heavy medium tank build the OKW player can't just laugh as their army actually benefits from this as their blob slowly morphs into terminators and they actually have to counter it with puma/panther/jadgpanzer play rather than sit and wait till KT to yolo finish the game.