Molotovs are more expensive, oorah is more expensive, penals have upgrade, you have to go for guards and/or ppsh doctrine as stock cons, while better, aren't going to carry you in late game.
Soviets do not have stock weapon upgrades other then penal ptrs, but nowadays there is plenty of muni sinks, given how every single ability cost muni now and there is plenty to use.
These costs stack up quickly if you keep utilizing them.
Soviet munitions costs are majority opportunity cost in nature where most other factions have nice one offs that elevate their baseline performance making them Mandatory for lack of a better term, their munitions overhead is higher so to speak.
The price increases definitely add up, but you can (and will) be decking out brit/us squads with 120mu in weapon upgrades, that's 6 Oprah's per squad. Hardly comparable, throw in pintles or HVAP or medkits or tulips or or or or or and there is a massive disparity leaving the Soviet with both more availible munitions and a lower baseline of power
Also nobody said that making barrage a vet ability means it has to remain as is, it could be free again or cheaper if it was restricted by vet