Profile of Maret

I think the AT capability of the SU76 is just not worth getting it due to better options. Buffing accuracy or pen on the other hand might screw Ostheer. If we want SU76 back in the meta (which it is not currently, as no one builds it), we should give back some utility. 20 mun barrage, as I said multiple times, is my suggestion.

I don't think that decreased cost of barrage make it popular. Problem as always in overall effectivness of unit. If you make barrage more user friendly (more accurate or more AOE) it could screw german infantry due to wipes and i don't think that this will be good in terms of balance and gameplay. SU-76 became a prey of soviet design - it trying to become good in any role, but fail, due to bad stats and more better units (Zis). It also don't have any chances in lategame - it means that it place in early-midgame, but as i previous said, these timeframes of games too short and SU-76 can't fit to it.
I recently saw Skippy game, where his team try to did heavy SU-76 spam - against 1 p4, 2-3 su-76 works, but when p4 2 or 3 or panther (or any another heavy) came to field, they light is off. While barrage quite effective vs blobs, SU-76 leaded to very later T4. And as result game was lost, because map pressure was lost and loses of su-76 leaded to huge fuel drain.

If it’s supposed to be a premium ATG, what if we made it so it could be killed by infantry from the back? It is open backed, and then it could get a buff to its damage (120 -> 160) or a cost reduction

It's squishy enough, if we make it more fragile, how you supposed to play and what compensated this? In game only rocket artillery very fragile, but it's compensated very strong abilities to wipe enemy infantry and team weapons.

I think about several possible ways:

1. Change of role could return it to game - make from SU-76 light howitzer for indirect arty support (what it did in real life). While T-70 is fast, moblie and aggresive AI, SU-76 became more defense-style, like mortar do.
2. Make separate upgrades for it. Like:

"Tank hunter":
Increased pen (+20) and damage (+20).
"Tank Hunter Ambush Tactic" stealth (with 1-st shot 10% accuracy and 10% pen bonus, rotation speed decreased by 60%).
Timed 20s (like HEAT OKW shells) ability to "Tracking" enemy armor (like m-42 munition ability). Barrage have increased cost to 45 and fire only 2 shells.

"Artillery support":
Give it more powerfull HE shells for "Supporting Fire"-increased cost of barrage to 45 and work like JT HE barrage.
"Piercing Shot" (like ISU-152 have with 50% penetration bonus).
"Smoke barrage".
Regular barrage become free, but share cooldown with "Supporting Fire". Penetration medium decreased by 10, far penetration by 20 to show SU-76 how infantry support unit.

Su-76 could equip only 1 upgrade.

Separate upgrades could help player to choose what he want - more AT specialized unit or more AI or still it like it is. Maybe add new ability for all variants like "Overdrive" that increased rotation speed by also decrease accuracy to slightly help to survive due low armor and health with bad pathing..

Alos don't forget about one trick with ppsh - you could buy 1 PTRS and icon of squad will still ppsh, that sometimes give you suprise effect.

The SU76 was OP in previous builds since it had decent AT capacity and a free AI barrage.
Both things got nerfed, now it's AT is only okay for tanks up to mediums and the AI is very situational and absolutely not a reason to get the SU76.
Now the SU76 is just not worth the price anymore. The only situation where I could imagine building it is if I play a T1 Soviet build, got blocked out of the fuel points and did not back tech in time when a P4 or Ostwind show up. Also I need to have no manpower to afford a back-tech and ZiS (about 500 MP in total)
If I need very decent AT, a ZiS + snare threat perform better. The barrage costs 35 mun and there's the same ability on the ZiS. Also back-teching costs only 20 fuel and not 75, so I delay a real tank only by a minute and not by 3-4.
SU76 should perform similar to the ZiS in my opinion. Or make the barrage way cheaper (~15 mun) with a bit longer setup time to make it worse against moving infantry, so that there is a real benefit from spending so much fuel. Now all you get is a more mobile, but way worse ZiS that also punishes you by delaying a tank.

Ye, it's all true, but problem with current soviet gameplay - all good things and upgrades lock behind T4. SU-76 don't fit to this design. Each builded SU-76 will delay you T4. It even don't fit to call-in strategy - because every builded SU-76 also delay your heavy on 75 fuel. It's like nail in coffin of your victory.
I like how Pgrens and Ostwind were returned to game. Pgrens now don't need T2 to build. Ostwind become really potent AI and AA platform. But i think for SU-76 there is no such simple decision. If we will change it's role on indirect artillery support - it could be option between fast mobile T-70 and fragile SU-76 with indirect fire. 2 potent options with different styles of usage.
Like in normal mode it fires low-speed HE shell as stug-e, on low distance. In focus mode become light howitzer (with another profile of shells) with increased range and regular and smoke barrage.

An SU-76 can’t be killed by a Grenadier riflegrenade shot like a Zis Gun, or suppressed by an MG42, or wiped by a flanking PanzerGrenadier squad.

SU-76 has a definitively different set of pros and cons when compared to a Zis Gun.

SU-76 can get crit engine from 1-st faust, MG-42 could use AP rounds to kill or seriously damage it. With crippled damage...it's almost dead unit due to it's low health, armor and pathnig.
Only one real pros from su-76 - you can't steal it. I never saw abandoned su-76.
But cons - low penetration than zis, low damage than zis, it will delay you t4 from terms of fuel (you need 75 to su-76 and 90 fuel to t4, i think choice will be very distinct and clear for su player), it have worse scaling with veterancy than zis. Zis also have the same abilities and range as su-76. Zis don't die from 1 tellermine.

In which situation you will be build su-76, not zis? Zis cost more MP, but give you much more potent AT power than SU-76. And if SU-76 have real pros players will build them. But now it's like old ostwind. You could saw one, when Mars in House of Orion.

I see only 2 ways for su-76:
1) It still in T3, but get buffed and cost increased to prevent spamming. It must become viable AT option, selfspotting and barrage must be removed, to don't get overlapping with zis.
2) Move it to T4 with completely different role - light howitzer.

IMHO i prefer 2-nd way. Because 1 clear role better than 2 roles. With all current 2 roles (light AT and light AI) you always have zis, but much cheaper and much stronger.
We also could evolving su-76 to low health version of stug-e. But i think it will be more cancerious option than everything else.

One of possible decisions it's just move su-76 to T4 and make from it light version of priest with low health and little possibilities to AT. Give it regular and smoke barrage. It will be completely different role, but at least it will be much better than current one.