Vet abilities are not a basis for balancing vanilla stats.
Its the other way around.
Vet needs to be balanced according to vanilla stats.
Arguing that Ost V1 negates SU85s native speed, is not valid, because you are applying additional requirements in an imbalanced situation
If you want to compare an Ost V1 vehicle, you need to compare it to a Sov V1 vehicle, not a V0.
It needs to be taken into consideration though or it will create more imbalances. The ability is there. If you will play carefully enough you will get it.
Imagine if they would nerf SU-85 so there is no problem, or very little problem to flank it. Flanked SU is a dead SU, no need to argue about that. Now PzIV will flank SU-85 with ease, kill it, get Vet1 in the process and start to be invincible. SU-85 will hit the field much later than PzIV, don't forget that. Soviet have to deal with MG42 first to be able to catch up.
Besides Panther will win against SU-85 1 on 1. If you can't handle SU's with PzIV, go for Panthers. The best tanks in the game. You will not be that late.
Of course I talk about 2v2 here as in 1v1 there is no excuse for you to not to dominate with PzIV.