I think at the moment the Soviets are fine with their anti-infantry, it's just the anti-tank part that kills T3 and forces what the german player hates is the SU-85. Just need a little diversity late game for better options.
I would like to get everyone's constructive thoughts on an idea of mine. Due to the lack of real at support in t3 of the soviet side, I feel like a simple fix might be to bring the SU-76 to t3 and buff it to be more anti-tank. I think by doing this you would have more options for combating german from their t3. Secondly if you bring the SU-76 to t3 you could nerf the SU-85 a bit and add a tank like the KV-1 or the IS-2 to the t4 to replace the SU-76.