Everybody knows that it sucks, but imo it didn't before it was "balanced". Last changes to su-76:
SU-76
The SU-76 fulfills the role of indirect fire support as well as anti-tank support. The AOE profile changes have improved the performance of its barrage, making it better suited at indirect fire vs. stationary targets.
Armor from 100 to 70
Rear armor from 50 to 35
Penetration from 93 to 100
Damage from 80 to 120
Reload from 2.375 to 2.9-3.4
Min range from 5 to 0
Scatter angle from 5.5 to 5
Distance scatter max from 10 to 4.7
Manpower cost from 160 to 210
Fuel cost from 55 to 75
Later the cost was changed to: 70 fuel, 240 mp.
If you look closely that looks suspiciously like a nerf: slight penetration buff, slight direct fire accuracy buff(but still can't hit infantry) and +33% dmg in exchange for about -33% rate of fire and moderate cost nerf. Imo, the cost is what makes su-76 bad currently.
Call-ins aside, before this nerf i would think: "mm, i can get one t34 or for 10 more fuel i can get two su 76" and the second option was not obviously worse. With guards button(now nerfed) and maxim support they were arguably stronger in defense department than one t34 be it against infantry or against medium tanks, also better at dealing with blobs and static defenses. Now you have to pay 40 more fuel for the same deal.
What is especially bad is that before this nerf you could expect to greet first panzer 4 with two su-76 on the field and third in production, now its one and second in production.
Anti infantry performance also greatly suffers form this as you need at least 3 or 4 to really make a good barrage (i believe barrage accuracy was nerfed as well but i'm too lazy to look it up).
Also, you can expect to lose some su-76 along the way given their fragility, and their health wasn't scaled with the cost nerf at all.
All this along with my opinion that this unit must be spammed to be effective leads to kinda like exponential decrease in performance. You lose fuel invested in su-76s faster while needing more fuel to get the pre-nerf effect.
So my suggestion is simple:
1). Decrease the fuel cost back to 55.
2). Make them deal 16,6%(that would be 20) damage on deflected shots so that they become somewhat viable in numbers against heavy armor(i'm 99% sure that tiger armor was buffed since that patch).
3). ???
4). PROFIT!
P.S. On deflected shots: So roughly: you can get 4 su 76 for the cost of one tiger(better have more but still). If they deal 20 damage while reloading about 50% faster than a zis, and zis have about 60% chance to penetrate while dealing 160 damage, they would be equal to about 1.25 zises dpswise against tigers front on non-penetrating shots. Seems ok.