As of right now many of the classes, vehicles, and abilities are just reskins of the other factions. I believe that each faction should have AT LEAST 1 (but preferably asymmetrical balancing would be maximized) unique feature that would be useful for their faction.
For example, Russians are currently underpowered because of how strong the German faction is (high amount of automatic weapons along with much better armor), the Russians could have slightly reduced respawn timer for squads that have 6/6 maybe 10s reduced to 8s or even potentially the reduced spawn timer being a commander ability. They could also potentially have larger squads than the other factions, These specific change would be historically accurate in the sense that the Russian army had served almost double the men that the German army did.
Another potential change could be increasing the rate of fire for the British bolt action rifles since they were known for the mad minute technique.
the game had more asymetrical equipments and should return to it, as it was also implied that some current loadouts (like all the MP40s in the german loadouts) are basically there to bridge the time until new and more accurate equipment is developed (like MP34s, G41 or other weapons for the other factions). Think the only weapon where that became true until this point is the FG.