Shreks are pretty terrible especially if overpriced at 90 ammo. their vet 1 is useful but nowhere the survivability other squads get when they reach vet 2 . basically every single squad has more survivability at vet 2 until the volks reach vet 5.
reaching vet 5 is a fucking chore. panzer fusiliers and obers (and pretty much every other okw infantry) have a much easier time reaching their veterancy then volks.
First of all: AT has always been great for units to vet up easily. Why? Because you are facing with "cheap" units an even more expensive unit. Reason why AT guns vet quickly.
Second:
This are the bonus for Volks.
-10% received accuracy
+30% accuracy -20% weapon cooldown
-10% received accuracy Healing when out of combat
+40% sight range +30% accuracy
-29% received accuracy
Not every squad get defensive bonuses at vet2 (Grens-Osstruppen-Conscripts-Penals-Irregulars-Obers-PF). Obviously an extra man is better on terms of survivability so i don´t think anyone would think that vet2 PG -JLI-Falls (-29% RA for a total 1.45armor) are more survivable than Volks.