Moreover, it's a serious question whether the Russkies, who were way overrated, could have defeated Germany The Russians would have eventually beat the Germans. It would not have occurred by 1945 without American help but they fought the Krauts to a draw by early 1943 with out any substantial help from the outside. the American aid spigot didn't really get going until the supply lines through Iran were open and the Northern arctic convoys were getting past the Germans.
I know a lot of people think this, but I'm not convinced. For one thing, I've run a simulation on the battle of Kursk without American bombing sucking some 30% of the German war effort away. If you apply 30% more air power alone to Kursk, the Nazis win. If you exponentially put all the 30% military anti-bombing effort in air power alone, or in tanks alone, Germany probably wins the Russian front. Moreover, with each three Jeeps you take away from the Russkies, you have to subtract one tank or two artillery pieces. They had limitations on what they could make. And remember, we supplied not only the ships that got them there, but kept the shipping lanes open in the first place, which itself would have required a large Soviet Navy. It's a ripple effect, and all of this presumes that without the U.S., Hitler would still have lost the Mid-east (he wouldn't) or that the Germans and Japanese wouldn't have linked up in, say, Iran. Now, that would be a problem.
I'd say it's 50/50 if Russia still wins without us in there---and a longer war very well could have led to an internal revolt vs. Stalin.