I'm far from an expert on the Soviets but I've always had pretty good luck with their Penals into Scout Car then Shocks build. The only problem I've run into with Soviets is their later armor is pretty terrible unless you go with some doctrinal vehicles. USF and UKF have much better late game armor.
What? Soviet armor may seem weak at first but is extremely powerful in combined arms...
the su85 is qualitatively disadvantaged to the firefly or the jackson thanks to the lack of a turret and slow speed... soo its likely to get soloed by a medium if youre not careful... but is cheaper and has slightly higher dps low target size and it can self spot... not really strong as an independent TD but massively powerful when supported
The T34 is less durable and much less survivable individually than the equivalent alled or axis medium (no escape mechanisms 20 less armor)... but is significantly cheaper and spammable... it wont fare well alone... just like the SU85... an enemy medium can easily hand a T34-76 spam if not supported... but when paired with an su85 or a zis.. the setup becomes quite potent...
the only real lackluster thing about the T34 atm is ram which should do a guaranteed engine crit imo...
The T70 is also pretty much the best lightank ingame...
The only real lackluster vehicles in the soviet arsenal are the SU76 and the M5 halftrack... both should prolly be taken a look at