the WWII map is simply unbalanced in general

Probably so. It's important to point out that the game has only been played 71 times, but seeing 10 (of 15 total) solos by one nation is a pretty glaring statistic even for such a small sampling of games. It's also important to note that the variant designer is relatively inexperienced in both game play and game design. It's an interesting enough concept, but it probably needs significant adjustments to be a map worth playing on.

yes I believe it is unbalanced. I've soloed twice with Russia in gunboats, and it's pretty easy due to the advantages. It is extremely easy to defend but also has substantial power and reach which makes it so easy to play in gunboats.

One thing that I think can be improved would be for Germany to have another coastal production center where he can build fleets (perhaps attached to Berlin, or in Cop or Denmark). This is because the center in KON is too much of a defensible position to be used for fleet production. This greatly limits Germany's ability to contend for Scandavia, since Kiel is really the only source for fleets, and it usually has to produce for both the east and west side of Germany.

I have to agree, I played the map 4 times, and the soviet union is the strongest with germany number 2. it takes cooperation between britain and italy to hold russia and that is usually not a long enough alliance.
soviet union is too strong. not by much. I like the map, don't over compensate if you change it.

http://lab.vdiplomacy.com/board.php?gameID=115

I am working on a new version to bolster france etc.

As Ruffhaus pointed out, I am relatively inexperienced at designing variants. Developers rely on feedback so it's important to take the time to let me know. Germany is supposed to be strong but USSR is definitely overpowered. I have taken Georgia away from them. France has gained a historic SC in Syria, but I don't know how that will affect Turkey yet. I also want to put a neutral army in Istanbul. All of these things require vigorous testing to see what happens

If anything, put a neutral standing army in Finland. No, make that two.
The Finns were a badass group of 'don't screw with us' woodsman. Despite being seriously outnumbered and ridiculously outgunned by the USSR during the Winter War of 1939-1940, they managed to retain their independence, with some limited concessions. One of their number, farmer Simo Hayha, became the greatest sniper in history, with 505 confirmed kills, mostly from his own sightless rifle.
A single Soviet army should have no chance of taking Finland.

I know where you're coming from, but along those lines almost everywhere would need a neutral army, especially Spain and Yugoslavia. Even Poland would need some, because the Polish didn't exactly surrender immediately either. I don't know whether a game with loads of neutral armies would provide the best game-play.

the target SCs have to be lowered. I have experienced as Germany that its only possible to win if you neighbors make fatal mistakes. Otherwise, they can very easily block you in the North Sea, the Caucasus, Constantinople, northern Italy and France...
gameID=13435

Just my attempt to inject some history of badassery. And, yeah, I think some balancing is needed, I apologise if I'm being unhelpful.
I think neutral standing units are useful in preventing growth at strategic phases, but I guess it would have to be done carefully on such a large map, so it may not be worth the bother. All the best with playtesting.