Idk about OP, I think that's up for discussion, but the concept that you can build a unit at minute 0 i.e. kubel, WC51, m3a1 and not suffer bleed because they use repairs instead of manpower is a....... dangerous concept to say the least. Although I'd say it is most definatly more map dependant how powerful those units are.
I think the Kubel and WC51 are properly balanced as T0/T1 vehicles as they allow to trade repairs against bleed but only at the price of being vulnerable to concentrated small arms fire themselves. What I dislike about the UC is how it can literally stand up to several (Volks)grenadier squads in heavy cover and win, and the Scout Car can generally do the same. For OKW there's no counterplay except building a Raketten or waiting for fausts and hope the enemy gets too greedy. I think concentrated small arms fire should do more damage to these vehicles.