It's definitely accurate to say that Stalin was as bad or worse than Hitler. Churchill was right about that, and Roosevelt too soft on Stalin.
Not sure it is fair to say the defense treaty with Poland caused WWII. It was certainly coming, Hitler had his eyes on France and Western Europe and the UK knew it could not stay out of a Franco-German conflict. I don't think declaring war in 1940 instead of 1939 would have changed anything. AFter all, the war until the invasion of the low Countries was called the Phony War.
But to get back to your point, I'm not sure it is accurate to call Japan and Germany the winners of the post war period. To begin, Japan has been in a funk since the 1980s and really hasn't recovered. Germany is admittedly probably the strongest economy in Europe.
But is that a bad thing? It was crushing war reparations after WWI and the Treaty of Versailles that crippled the German economy and lead to the collapse of the Weimar Republic. Japan on the other hand never was able to modernize its economy or social systems to keep up with a modernized military industrial complex. If there had been a strong middle class in Japan, would the militarism of the 20s been prevented?
I'd argue that the winners of WWII are just as they appear: the "West" and in particular the US, Canada, the UK, Australia and NZ. Putting commonality of language aside, those countries have the robust economies, and protections for individual liberties that are most attractive to folks like me (and I think the folks on this board).
We have our squabbles here on this board, but at the end of the day, we -- Yank, Aussie, Brit, Kiwi, Canuck -- are far more allike than any other group of countries that derive from the same cultural source. Hell, look at South and Central America, or China/Japan/Korea for an interesting contrast.