Then they should have put in the SU-100 instead and made it cost the same as a panther.
http://en.wikipedia.org/wiki/SU-100
The SU-85 was actually similiar to (worse armor wise, similiar damage wise, a bit worse range wise) than the stug IRL. The current in game SU85 is more like the SU100 than the real SU85. Maybe then just make it more expensive and call it the SU100, but it is too good for its current cost.
The lack of other viable "tanks" (note SU85 and stug are td's not tanks) in the soviet arsenal is not an excuse for SU85 being op. Then they have to give the soviets a better T34 that can stand up a little better to p4's or one that is up-gunneable to 85mm. The current T34 is most useful for ramming which was an extreme rarity on the eastern front. The T34 was not as good as a p4, but it certainly wasnt a battering ram.
I agree with your post, i was stated a reasoning not expressing how i think it should be, the only problem i see with nerfing the su but buffing the t34 is the fact that you will -never- have both in a competative 1v1, my suggestion is to slightly nerf the su 85 and move it to t3, that way it still has the same timing but being less effective means a good secound tank would be the t34 (which should get a slight tweak to its cost effectiveness).
Or throw make the teching system alot less dumb, yes i really dislike only being able to use 50% of my units per game)