It's very difficult to say what you can do to soviets without major reworks. Penals and conscripts will always fight for their slot as mainlines, and if penals are not OP, they will not be used because they're behind a very AI based tech structure that pushes you out of AT practically.
I'll wait a bit to see what other people say about the faction, however I think although the T70 is easily the best light in the game, I don't think it requires a change. Its damage is decent and cannot be ignored, but being properly prepared with mines and AT guns can hamper any LV well enough.
