Cheaper tech is not actually an advantage with the fuel penalty . and vet 4 and 5 is rare on units besides volks its not even worth mentioning.
Show me the other factions that can actually get all of their tech then.
(You can't. They won't ever because it costs them even more without the fuel penalty than it does for OKW.)
And vet 5 isn't hard on infantry units, it was fairly easy six months ago until everything on legs gets wiped constantly now. The vehicles are definitely harder though - I'd regard the Jagdpanzer IV as probably easiest of the vehicles to earn it. I'd be pretty happy with reducing the XP requirements on OKW vehicles to make vet 5 a bit more attainable.