That's not even the SU-85's fault, that's just bad players misusing the unit. It's a Tank Destroyer, not an Assault Tank. A Jagdpanzer driven into the enemy by itself can be killed by Conscript's AT Grenade + T-70, but that doesn't make it UP.
You are right, it's not the SU-85s fault. The SU-85 isn't even a bad unit in my opinion. It's a long range turretless tank destroyer and it does its job well.
The thing is, you just can't fit the unit into a proper game plan without either leaving significant weaknesses in your strategy. If you use a makeshift combination of SU-85s+call-in tanks to fill the gaps you are just doing something that can be done both better and earlier by teching to T3.
I've said it before and I will say it again. The soviet tier construction is poor. T3 gives you 2 light anti-infantry armor units (redundancy) and 1 solid medium tank. T4 gives you arty, a tank destroyer, and a hybrid of the two which is useless as you can get better units for the job in the same tier. T4 just gives you 0 attacking potential and the katy is not good enough to sustain a defensive playstyle. Swap the T70 with the SU76 and suddenly both tiers will work and these units will actually have a significant place in the game again.