I think the game is close to balanced, but there is good reason to think it might not be.
basically, if russia were any weaker (or either axis player any stronger), there might be a high number of games where a) novice players would have a terrible time as russia gets pwned, or b) early bad luck by russia would allow for allied defeat even with superior play.
In other words, if germany has the ability to force a battle early in the game against the least resilient allied power, then even when played badly the axis always have a chance of an upset win in that battle. The stronger you make the axis initially, the more risk that the game is decided by luck in spite of any allied skill very early on.
Having said all that, I think it’s pretty darn balanced and I’m just suggesting theories for why it might intentionally have been left with some imbalance.