I'm not sure if I agree with you when you say "One on one against Germany [Russia] lost." By the end of the war in the eastern front the Soviet Union had just dealt Germany two very major defeats at the Battle of Stalingrad (despite the fact that the entire city was leveled) and at the Battle of Kursk. Hell, Russia completely demoralized Hitler's tank army at the latter. It wasn't just about overwelming the Germans with soldiers either; while Russia didn't really have a pot to piss in for the most part, they had some pretty damn good tanks.

However, would the Germans have defeated the Russians had the US not gotten involved on the Western Front... probably.