Volks have inferior stats, but cost less than everybody else but scripts. They also never pay to unlock abilities, and have 5 levels of vet. What infantry other than they have these advantages? They are stopgap infantry, and with STG's seriously threaten unupgraded Allied infantry now.
I encourage you to show me a game where you are capable of substituting SP's for volks. The reinforce cost, the high initial cost, and the limit DPS at range make them very vulnerable to infantry. They are also 4 man squads and their vet does not give them predominantly bonuses that assist in combat, but they get bonuses that assist in repair or healing at vet 1.
Vet 5 means little if all vet 5 levels combined are still inferior to allied vet infantry. and yes sp's are a bit more expensive but their reinforcement cost is equal to the gren. allied infantry excel at short range (safe for is) and any long range combat will be won thx to the mg34 and later obers.
Your correct that upgraded volks will beat allied infantry but sooner or later your volks will get outclassed and become a huge mp drain.
Suffice to okw with its weakest support units and lv's should have the strongest infantry. vg's need to be able to hold their ground against allied infantry. they need a 90 ammo upgrade with damage similar to regular sp's
I mean WTF is going on here. weakest mainline infantry weakest support most expensive tech overpriced units. OKW is not doing so hot. The shreks on volks was able to mask these rather large prbolems for a very long time but now the okw needs buffs and a lot of them.