I can't say, that USSR weak. But IMO USSR T1 and T4 have problems.
T1
T1 looks like appendix. I am still sure, that T1 should be removed, and units from it replace to another Tiers. For example:
T0 (HQ) - Engineers, Conscripts, M3A1
T1 (Previous T2) - M1910,PM-41, ZiS-3, Sniper
T2 (Previous T3) - No changes
T3 (Previous T4) - Penals, T-34, SU-85, BM-13. Penals have some of their vetbuffs moved to stock.
T4
Units from T4 are mostly non costeffective.
T-34 is peace of crap, it can missed in very-very-very close combat, have weak armor and speed as another medium tanks. Concept of suicide tank for low price is good for doctrine, but not for unit from top tier of faction. #T-34CallInT-34-85NonDock
SU-85... I think it need rebalance. It shoot fast, but don't penetrate often. And its price is close to price of M36.
BM-13 I don't see any big problem hier, maybe only increase AoE a little bit.