Adaptation is the name of the game but if you get a unit that comes early and can deal easily with lategame units, you know there is a problem.
If I get Luchs killing IS-2s frontally reliably, no one would be happy.
Balance in a game is all about risk vs reward. The risk in playing out SU-76 is relatively low compared to proper AT guns, but the reward is disproportionally high. That's the main problem with it.
I mean fine if it performs well early-mi game with decent damage + free barrage as it should. It's the endgame performance that I find ridiculous. Buff the SU-85 if it needs a buff by all means.
EDIT: Like in VCoH, Tier 3 in sovs is designed for Early-midgame performance. M5 is the same in both Americans and Sovs, M8=T70, AT = SU-76 except the sovs can get AT and SU-76, SU-76 is mobile and SU-76 has barrage. There is no justifiable reason IMO to give it the endgame performance it has currently.
Su-76 performs well against vehicles, even heavier ones, agreed, has that barrage ability that can kill infantry, appears on battlefield pretty quickly, and can be spammed.
Agreed on all that.
But it has a peel, not an armor, has no turret => it is quite vulnerable. What a soviet player would do? He has the choice of relying on T3 vehicles and wait for call ins in late game like KV1 s, Shermanns, ISU, IS-2. If he wants to have a powerfull army he cannot rely ont T3 and T4 both.
I am telling you that if he relies on T3, he is quite exposed. No doubt quad + su-76 is a powerfull combo, but would that suffise to counter late game german armor? I would say no. Both axis factions have enough tools to deal with su-76s. Considering the efficiency / vulnerability ratio, is Su-76 realy OP? We don't count stugs as OP, do we? Flanking armor will erase all Su-76s on the map, guaranteed. And quickly.