If must say...M10 and Stug3 need medium tank tech.....for balance it coming later so have 160 damage is fine,but look su76,as light TD,is coming later than OKW puma,and cost more,for now even it vet 3 it not have 160 damage so it useless in late game.
For those TD like M10 and Stug3 in late game they default 160 damage also could punch most medium tank,but don't forgot Allied without commander and UKF Comet and Churchill not have tank HP more than 640,so Allied should have more powerful TD against German heavy,but still that problem,SU76 not have enough damage to use even in VET3,even vet3 it can not beat new Stug3.
The SU-76 has a dual-purpose as both a light AT vehicle and as an AI vehicle through barrage. That's how it scales.
It outranges and outpenetrates both the M10 and Puma as well. People talking about the damage as though that is the only component of AT performance are being kinda dishonest at best.
The SU-76 struggles because it simply doesn't have a place in the SOV arsenal, nor in the timing that it arrives. I've said before that it would be much better off being made a "pure" AI vehicle, like the STUG-E or even the Scott rather than bothering to try and make it's AT performance better. If you want lategame AT vehicles as SOV you get an SU-85.
Also: Are you seriously using the Stug against allied heavies?