SU has high pen and range, you support it with your inf, so Panther can't hunt it. You use PaK to counter it, or a good offensive.
T34 is there to destroy the support. It is good versus inf, good versus PaKs.
There are no real counters in CoH. The game is mainly based on micro. Sure, there some situation you can say, it is a counter. Like PaK versus SU85.
Day for real stories, when i know that in CoH no any counter. M5 with quad don't counter planes. P4 don't counter t-70 or t-3476. Minesweeper don't counter mine. Faust don't counter M3. MG don't counter infantry. Rocket arty don't counter blobs or team weapons. Obers don't counter cons. Stormtroops don't counter engeeners or grens with volks on close-combat. It's all matter of micro.
What else you will say for me?
SU-85 top-tier TD, you want for stug be in pair with SU-85? Move it to T4, boost stats and price to 130, change abilities. I also want that SU-76 was hardcounter to P4....but BALANCE. You have panther.
If you use 1 panther against hiding SU-85 it's your fault. No one SU-85 in the whole world never will dive to full-healthy panther (i don't consider noobs). But if you do it with your panther - Yolooo!!! I panther!!! Or f..k who planted mines here? What these guys want to do with this AT grenade? Which it's fault?
If i will dive by su-85 to panther which it will be fault?
Against t-34 use stug. You support it with your inf, so t-34 can't hunt it.