B4 was our first choice.
However, the commander needs something reliable to crutch onto, since every other ability is situational.
There is no way to make B4 work reliably, without either making it look weird (e.g., B4 shells dealing same AoE as ML-20), or letting it perform like a complete RNG cannon, which would ruin the doctrine.
There was also always the danger of overbuffing B-4 and forcing players to fight vs waves upon waves of Counterattack/Tank-Hunter tryhards.
Why not try to give the Soviets access to HEAT or HVAP rounds for medium tanks/TD in this commander, I think it would be very thematic.
They will be boost some damage/pen but totally usless aganist infantry, it can be a timed ability same as Elite armor doctrine or two switchable rounds as on USF Sherman.