Cmon, the unit is just fine. The barrage ability is OP and has the same pen as the STUG, but with 10 more range.
it has both inferior damage AND penetration compared to a stug. Barrage ability op? says who? Maybe if you let your infantry blobs to play volleyball with the grenades.
The unit per se is "fine"
The t-70 is an anti everything tank short of medium tanks, 444 and puma that obliterates infantry squads and it's insanely more popular, Zis is the best at gun in game and the t-34 can be easily accessed after tier 4, and on top of that Guards can soft cou ter light vehicles pushes, so the su-76m has no place among all the much better and safer options.
It should actually be nerfed to 50 range and lower penetration and have a 10 fuel cost reduction so it can be used as emergency AT vehicle
The SU-76 lacks firepower to be a tank destroyer, and is useless against infantry (the barrage is overrated, its long cooldown makes it harmless every minute or so). Its outclassed by both the static AT gun and the SU-85, the latter of which is fine. It even struggles to kill light vehicles at times, due to it being a casemate with mediocre tracking.
the suggestion to nerf it is completely stupid, unless it gets pin point perfect on-the-move accuracy, it would be even more useless than it is now. They should simply keep the current stats and buff it's anti infantry (SPG ability), or make it a good pocket TD (stug)