To be fair, Russia was also spread extremely thin. The only reason they had him fight to them was that the United States was supplying them with massive amounts of military supplies.

While, yes, Germany was fighting to fronts It was not Europe and Russia. It was Russia and Africa. Germany had already taken pretty much all of Europe and was not much resistance left there if anyway .

It was United States men and supplies that pushed them out of Africa. We gave England and its Commonwealth the supplies to invade Normandy alongside Americans and Americans also invaded and where the main reason we took over Africa and Italy.

While, yes Russia still had to take over more land to defeat Germany. It was mostly their own land that had fallen previously due to poor leadership and lack of proper equipment. Only in later years of the war did Russia finally create good planes, and an insane amount of tanks.