The Red Air Force was pretty significant as well.
Plus, Mother Russia had, what IIRC Zhukov said, "lots of sons".
The Germans were ground down in the east by superior numbers.
Now, if the Germans didn't have to deal with the West then the Eastern front has a different outcome.
Convert all the steel of the U-boats into tanks and other AFVs, put the fighters and AAA guns that dealt with the 8th Air Force and Bomber Command into the Eastern Front, take all the resources used to build the Atlantic Wall, and the German's chances of victory increase.
"The German Army in fighting Russia will be like an elephant attacking an army of ants. The elephant will kill thousands, even millions of ants, but he will in the end be overcome by their numbers and be eaten to the bone." - Colonel Berndt von Kleist