Vet. 5.
Which is inevitable as long as you keep them alive and fighting, regardless of them being upgraded or not.
I'd rather have to get Volks to get 5 upgradeless than REs to vet 3...the first one you can actually intend! REs getting vet 3 without weapons feels like an accident it happens at all.
Bro, do u even play this game at all?
Do you know how and why volks vet up fast, and why they are the units you can see (more often in comparison with other units) at higher vets?
It comes from the damage they deal using their shrecks bro!