Maybe don't use such arguments and just suggest your ways how bring unit in-game? You want make from SU-76 sniper-hardcounter against mediums? While Su-85 will be potent only against big targets like P5 and tigers?
While it possible way i also see some troubles with it - "hardcounter" su-76 against mediums in T3 will ruin OST gameplay and maybe OKW too (spam of T-70 and su-76 without T4). "Hardcounter"Su-76 in T4? If it will be cheap (like now) it will be spam, if we will increase price than we must changed all stats too (like armor, health). Armored su-76 with open top? Very funny...
Also before your answer - what means "hardcounter" for you? For me - unit that designed to fight against some kind of target with excel effectivness. Like sniper against teamweapons, ATG against armor, stug against mediums, puma against LV, rocket arty against blobs. Also don't forget about timeframe. Each unit good in right time.
This is becoming rather specialized and I will give a general answer:
Imo there two types of TDs should be created. The heavy TD meant to deal with Super heavy tanks like KT/IS-2 and the the medium TDs meant to deal with medium tanks.
Su-85/FF/Panther/M36 should be in that category while Su-76/Stug/JP in the medium TD.
One could increase the target size of super heavier and reduce the accuracy of heavy TDs so that they can hit the Super heavies but perform worse against mediums.
On the subject Su-76 there many changes that need to take place to create room for it. An an example one could:
1) Delay Ostheer T4/OKW Panther and Super heavies so that there more reason for player to invest in meduims
2) replace zis's vet 1 tracking ability with the barrage. This change would make both SU-76 barrage more attractive and mortar more attractive.
3) Replace Su-85's vet 1 tracking ability with the focus sight. There combination of focus sight and tracking is simply broken and now Su-76 bring something unique to the table.
4) Reduce the accuracy and ROF of the SU-85 and change it's vet bonuses to provide penetration bonus so that it perform better vs KT type of units
With these changes people would have more reason to invest in medium tanks and more reason to built medium Tds.