If the SU-76 isn't good against mediums, what's it for?
Its casemate design makes it suck against lights (which'll just circle-strafe it) and it's too small to fight heavies.
Su-76 does not need 100% chance to hit PzIV at range 60 (max) to be good.
Accuracy that is so high is simply broken.
You can watch this replay and debate SU-76 performance with Frost.
In many cases Soviet unit have very powerful vet bonuses and if one buff their base stats one also has to nerf their veterancy bonuses.