Their main advantage during Berlin specifically was their numbers and their artillery. If Darkflow was smart, they could’ve made each campaign different, with each side having distinct advantages and disadvantages.
Berlin Soviets: Had the number advantage, so give them extra reinforcements.
They also have the advantage of what I can only describe as unlimited arty spam. Make the arty wait time shorter than usual. They make their arty have a larger radius due to their guns’ large caliber, up the number of shells shot (the larger the shell, the more inaccurate it is), and up the arty damage so it can kill tanks due to the gun calibers.
They can have many tanks in battle but are countered by the Germans having an advantageous defensive position and their access to late-war tanks (Tiger is to be moved to lvl 24 behind BF 109, Tiger II is to be moved to lvl 31, and Tiger II H is to be moved to lvl 35. This will be balanced by the Soviets having a reinforcement advantage and having early access to attack planes and fighter planes for bombing). Even if the Soviets are spamming IS-2s, the Germans will have access to 88mm guns (making them into emplacements may be the best option for balance) to counter this.
Soviets had air superiority, so every plane should be unlocked from lvl 24 to lvl 27. Due to the Luftwaffe being virtually non-existent, except for a few suicide runs during Berlin, Axis should get no planes until at least lvl 19, the most being lvl 27. Limit Soviet vehicles to wait for 2x as long after dying for premium players so that they suffer (they are spammers, and there is no balance for them due to their constant spamming), and other people get a chance to play as a vehicle. Standard players will get the usual wait time.
Axis: They could equip many of their troops with advanced weaponry. They could do this not by a large amount of manufactured weaponry but due to having such a low number of troops that it made them look plentiful. Leave FG 42s alone, lower the VG 1-5 to lvl 14, the Beretta M38 to lvl 20, the MP 43 to lvl 26, and the STG 44 to lvl 32. To balance this firepower issue, give the Axis reinforcements and make it dramatically less (possibly half the amount of Soviets or less, depending on how well you accommodate the defensive positions). Also, Panzerfaust 60 should be lvl 3 or lvl 4, and Panzerfaust 100 should be at least lvl 15 at the most lvl 20.
Make Axis Arty a longer wait due to ammo shortages. Possibly make the radius smaller due to them using mortars a lot since their big guns are long gone, so it would have to be mortars being used (I am not familiar with their artillery during Berlin, but I am sure someone does, and they can make the adjustments to that).
We covered the Plane issue, and we covered tanks. I could do the other campaigns, but I am not gonna 
Obviously, this needs to be tested first, but some form of this has to be implemented so that you don’t have to buff one side to make them overpowered so that they can compete. There are different ways to create balance without making one-half of the player base suffer. Not every campaign in this game is made for symmetrical warfare; the Russian devs have no excuse for this due to their country literally turning the tides of WW2 due to asymmetrical warfare in Stalingrad.
NO EXCUSE DARKFLOW, NO EXCUSE