IMO, historical balance is the last thing PDS will fix. The same goes for any historical mod which is constantly being developed with cool features and events. Problem is that balance is affected by every single defect in the code or script, so during the endevors to fix bugs, the balance is constantly changing for better or worse.
Best thing I can recommend is to play a hands off game, and watch where the AI is at throughout the game. For GER/SOV for the example, check out the early 1943. If GER hasn’t penetrated deeply, SOV is overpowered. If SOV is at Berlin in 1942 (I saw this in my first historical HO game in 1.5.0), then SOV is way OP. Or if Jap defeats CHI by ‘38, ITA loses Africa by ‘41, etc. You get the drift.
Anyways, at that point start another Hands Off game but add country specific buffs in the Strength Sliders prior to game start. Try again until it much better resembles the real war. THEN start your game, and give traditional enemy countries even more buffs and reduce strength sliders if added for traditional friendly countries, all according to how much of a challenge you want.
I love to play the USA, which absolutely sucks from the point of balance. As the last major which gets involved, the entire world needs to be well balanced by 1942, just to get into a war which somewhat resembles history.
I wrote a mod for BICE which they merged into base BICE, which even added axis minors, allied minors, and Brazil (which in some mods turns into a power house), and added WEAKEN sliders as well, just in case you want to win the entire war by yourself.