Relic would have to increase the cost for both tier buildings then because their current cost would be too low.
I think it's fine the way it is. A T-34 can arrive at the same time where an OST player can get a T3 vehicle himself and it counters Ostwinds and (with flanking) StuGs. And it's easily replaceable (although I'd like to see its pop cap reduced to 8).
You don't need to rush T-34s anyway. Against enemy medium armor you can get multiple SU-76s.
I have to agree with Gabba here because if Soviet T4 did not require T3 then T34s would dominate since they are cheap and are going be effective in numbers. Also if you go to T4 you can get a T34/76 the same time an ostheer can get his p4. Imagine if Soviet T4 could be built right away, T34/76s would come out and maybe wreck ostheer before his T3 vehicle can arrive since T3476s as they are 80 fuel since they are crap they can destroy in decent numbers produced.