Re: oh yeah
Getting back to the original point, I think it took both the American and Russian effort to defeat the Nazis.
At the time of the D-Day invasion, Germany had about 3 times as many divisions on the Eastern front as it had in the West. And still, even with overwhelming air superiority, it took the Allies almost a year to make it through to Berlin. So, if the USSR had been taken out of the picture by then, and if the German military hadn't been bled dry in Russia, then Hitler would have been unchallengeable in Western europe.
On the other hand, if Russia didn't have the benefit of a constant stream of war materiel from Allied convoys, (and possibly, intelligence from the Enigma code-breaking effort) it is unlikely they could have turned the war around on the Eastern front. The sheer size and depth of the country may have eventually ground down and halted the German advance, but decisive battles such as Kursk, could never have been won without aid from the West.
Any analysis must recognise the enormous contribution of the USSR in terms of lives, some 25-30 million, and, also, the contribution of Allied, mainly American, industry. Just one example; at its peak, the Americans were manufacturing almost 100,000 military aircraft per year. Without both of these remarkable (and different) contributions from the USA and the USSR, the outcome of the war would have been vastly different.