Profile of nee

Friendly advice: don't edit the first post, just state that it's the original idea and has been changed, referencing to a later post.

My thoughts on the matter:
-One way to make Commissar unique from other officer squads is utilize Mark Target like OKW's Command Panther's ability: costs munitions, requires unit to target, but otherwise works just like Mark Target. That way, rather than requiring elite infantry, you cause ALL your units to work like elites for a short time...provided they're attacking that particular unit. That Commissar comes very early makes this an early advantage, yet also assists late-game against things like Tigers. Commissar would have to be kind of durable as well as cheap though, especially against suppression, squad wipes and heavy tanks means this ability is pretty much all that makes him good.

-I'm kinda OK with the heavy mortar, not too many commanders feature the unit. Would negate the KV-2 though, which is a far more niche call-in given its precarious stats and capabilities.

-For the truck, I think it should have some uniqueness involved. Seeing as you're against forward retreat, there really isn't much else outside of Opel clone, which IMO Soviets don't need. They need the manpower to field units, not manpower spend to give more munitions and fuel It's understandable if the intent was to let the player float munitions to spam that 240mm barrage and KV-2, but then that's pretty much it.
Some suggestions on the unit: give it repair ability so it acts like a mobile repair station (must deploy, refer to original USF M3 Halftrack idea in Ardennes Assault);
Observation upgrade: basically has Spotting Scope ability, when it's not moving it has 2x sight range, excellent to help your units find the enemy, make it deployable so it doesn't accidentally move due to pathfinding faffery; make it combat-oriented bonuses when deployed in specific sector, similar to original P4 Command Tank's buff, which justifies its flimsy armour and need to keep it hidden and away. Also, a camouflage toggle that helps preserve the unit.

-TBH I prefer ISU-152 over KV-2, the former has longer range and can engage targets behind your other units, that's more useful support than KV-2 which needs to toggle its siege mode and encourages camping rather than pushing forward for those VP points.

-Bit of a wild off topic miscellaneous idea: reintroduce M-42 AT gun but give it some powerful support abilities like button or tread shot. It won't one-up tanks by itself but trapping enemy tanks would allow your other units to easily kill it.

I can't say I like the 152mm barrage idea, it sounds basically like one-click anti-blob/ flank attack ability that requires munitions and a working right hand, rather than units and a brain that can micro troops. Fear Propaganda Artillery can do the same thing, even if only against infantry (plus AT Guns, when's that gonna be fixed? 2019?), and there's also the PTAB bombing run that stuns enemy vehicles and damages infantry, or Incendiary Barrage. Given that you already have heavy mortar/ KV-2, a conventional barrage seems redundant, which is why I prefer complementary abilities that inflict things like stun or burn ground. IMO a better idea is an ability that rewards your units with kills and veterancy, rather than the other way around.

Aren't these abilities referred to as "offmaps"?

Odds of a team calling in airstrikes at the same time at the same location, notwithstanding the odds of both players actually using abilities simultaneously, and have the munitions to pull that off, are a bit isn't it?

Also this would naturally progress to "omfg back-to-back fear prop artillery against 4 Soviet opponents."

Valentine and Sexton were obviously designed to be used together. Problem is, not only is that rare in itself, but only really when you have multiple Sextons, and the Valentine is at vet1.

Some simple changes:
-Sexton can be used when you activate Coordinated Barrage like the base howitzers;
-Coordinated Fire ability can only be fired in LOS, but includes any Sextons on the field, it encourages both Sexton use as well as using Early Warning first;
- Valentine's vet1 ability causes the Sextons to fire airburst/ WP shells
-Misc. idea: Supercharged Rounds that greatly increase maxmium range

Give it Canister shells at vet1 (copy from Greyhound), and/or give it Treadshot or Aimed Shot (copy from AEC/ OKW Puma)

At least then, it's still no killer but it's great way to complement your other units.

Also WTF is it with people demanding a 100mm Soviet unit?

I'm unsure how to buff this unit:

Buffing it's AT/ anti-cover firepower makes it more desirable but also makes it compete with AA halftrack, for better or worse, especially if you balance this with increased cost or upkeep etc.

Personally I don;t know why Relic went for a .50 unit, as they were largely AA/ versatile defensive weapons. The .30 was the usual HMG role, and we already have sound and Vickers as base model for it. Reminds me of playing Bioshock 2, when you had a "measly" .50 cal minigun that did basic (re little) damage, as an early weapon.