It was certainly Stalin’s view that the Western Front in 1944 was far too late.
He was already moaning about the absence of a second front as early as November 1941, barely a few months into his war with Germany. http://trove.nla.gov.au/ndp/del/article/41937421 See if you can find Britain moaning about the USSR not opening up a second front 1939 to mid-1941.
Stalin sent Molotov to Washington in May 1942 to encourage the Americans and Britain to open a western front in 1942 to draw off about 40 German divisions.
Stalin spent the next couple of years pressing the Western allies to open up a second front, and in other respects seeking their assistance such as requesting bombing raids on German targets to assist Soviet troop movements.
You’re out of your depth with your ill-informed assertions about how the USSR won the war by fighting in only four of the six years of WWII in only the eastern European land theatre. There was a bit of fighting going on elsewhere, not to mention some rather significant logistical matters which also exceeded Soviet production which was conveniently limited to that land war while the rest of the Allies had to fight on land, sea and air around the rest of the planet.
What does this have to do with the defeat of Japan by the glorious forces of the USSR in a few days of battle at the end of what the Western Allies thought was the Pacific War?
You assert that the USSR won WWII all by itself.
Japan attacking the USSR is irrelevant as you say that the USSR won WWII all by itself.
By the way, could you explain why there weren’t any Soviet occupation forces in Japan to cement the magnificent Soviet victory, all by itself, over Japan?
Also, why were the glorious forces of the workers’ paradise conspicuous by their absence in North Africa, Malta, Sicily, Italy, France, Belgium, Holland and so on as the USSR won the war all by itself?