... Weren't the Allies basically down to England or something, and Russia was under siege and starving to death, feeding its soldiers sawdust, and Poland was pretty much wiped off the map again (but still resistant, as so many people seem to forget), France occupied under a puppet state, Spain fighting a fascist civil war, many of the Scandinavian nations "working" with Hitler because they didn't want to be invaded (for example, Finland was involved in the terrible siege of Leningrad), Japan hopping its way through China towards the other side of Russia, and so on?
I'm actually just replying to provide a few pedantic details. That I'm replying only to one paragraph hopefully indicates that I actually agree with the majority of your post, not that I think putting forth a few random corrections completely undermines your whole argument. Actually, the fact that, on the internet, the latter is the usual meaning is why I'm typing out this very disclaimer.
Anyway! A major thing is that Japan didn't seem to have much interest in invading the Soviet Union (and it wasn't until Stalin realized this that crucial troops were moved from the Eastern border to the front with Germany). Their whole alliance was kinda weird; as far as I can tell, the only major effect it ever had was getting Hitler to declare war on the US (something he wasn't actually obligated to do, IIRC, since Japan attacked first), which is probably for the best since even then there was a significant pro-Nazi segment of the population in the United States. That's the major reason for the conspiracy theories that FDR let Pearl Harbor happen so that he could get a war with Hitler (they're ludicrous because Hitler declaring war on the US was a batshit insane move, and it's unlikely that FDR could have gotten the political momentum to get the US to declare war).
Russia by this time had JUST begun to mount a counteroffensive, and was looking pretty fucked. The US didn't actually enter the Western Theater, though, until about the time Stalingrad was turning around in the Soviets' favor. Until this time, US involvement was almost entirely economic, and most of that seems to have gone to Britain. At least given my understanding, Hitler was never going to win in the USSR, whether the US helped or not; between his own inability to let his own generals make decisions on their own, Stalin's eventual decision to let
his military run itself, and the gigantic natural resource imbalance, the major reason for the USSR's initial losses were because Stalin had just had all his best officers executed.
France had its own significant resistance (which, for a while at least, harbored a lot of the Polish codebreakers that were crucial to Britain's complete and utter dominance of the military intelligence part of the war), the Civil War in Spain was over but Franco wasn't optimistic about Hitler's chances and just kept non-committal throughout the whole thing.