You must all understand, that the reason the soviets were turned into an OP country, was because, quite simply put, back in all the other iterations of the HOI2 engine, from vanilla HOI2 to DH, the soviet union was a pushover for germany. And in the old forums, and everywhere else, everyone complained about how the soviets were so easy, so killable, etc, etc. Back then, an average player could spam 1 unit type, and swamp the russians easily.
DH came up with the answer of 'fine, you bastards, we will give you a challenge' and basically gave the soviet AI the equivalent of horse steroids, what with the likes of 0.1 cost units, faster building and IC bonuses and an incredibly agressive AI. The result comes off as the opposite now, that the soviets are too OP. In truth, there can never be that perfect balance that people will be looking for. As humans, we have the chance to exploit the game engine to our benefit every single time, so as to never quite lose. First time players that are learning will lose many many times to the SOV's, until they understand just how the game works, and then they will begin the painstakingly long process of becoming Eastern Front vets. The result of this is that players will not try to exploit the engine anymore, and instead give themselves heavy handicaps, rather than maluses. Me, for example, i have the no-rushing-moscow rule, or the no-front-encirclement rule, as well as building all kinds of units rule, rather than just the necessary ones.
It all comes down to the fact that each player will have to find his or her own balance of challenge for the game.