The StuG is designed as a bread-and-butter tank destroyer for Ost, and matches up well against most armour in the game. However, it loses to its fuel cost in call-in heavies like the IS-2 because of its relatively low penetration, making building what should be a fairly standard unit a risky play.
The SU-76's initial design was a dual-role artillery tractor / light tank destroyer. It had a weaker barrage than the ZiS gun, but it was free. This turned into a problem in team games when players figured out they could buy loads of them and nuke any unit that came close by stacking several barrages on top of them.
The solution was to give the SU-76 the ZiS barrage (which costs munitions) instead. It was a good idea in theory, but taking away the SU-76's ability to act as an indirect fire weapon killed it off: the T-70 already beats everything at that timing that's not a Puma, and the SU-76 isn't guaranteed to beat that.
I've got a solution for each.
StuG
- Replace the StuG's ineffective HEAT shell ability with a timed AP shell ability like its closest parallel, the M10, has. This'll allow veteran StuGs to engage heavier targets when vetted up if you pay munitions.
SU-76
- If it's meant to be a hybrid artillery tractor/tank destroyer, scrap the ZiS barrage and give it the ability to switch to an anti-infantry mode. Something like the StuG-E's shells should do it. It then becomes a more defensive alternative to the T-70.
- If it's meant to be a tank destroyer, raise its cost to 280 MP 90 FU and give it 160 damage. If it's a ZiS gun on tracks, let it be a ZiS gun on tracks.