If Hitler had pulled every single one of their troops and tanks from the west and from Africa and sent them to the Eastern Front, it still would not have mattered. Why? Because all of those added together
might have equaled what, maybe ten, twelve more divisions...and this was a relative drop in the bucket compared to the forces involved on both sides. What killed the Wehrmacht wasn't the quality or quantity of the troops - it was the logistics. It had an ever-lengthening supply line hampered by the different rail gauge and by partisans and - especially - by the incredible amounts of mud in the spring, and the bitter cold in the winter. The Soviets' supply lines, on the other hand, were getting ever shorter, and so it took them much less time to get what they needed where they needed it to go...and the big enabler in this was Stalin's order to move the thousands of factories back to the Urals.
And besides, by the time our bombing campaign against the German homeland was really beginning in earnest, the tide had already swung in the East. The first big bombing raid was against Cologne on May 30, 1942, but the battle for Moscow - the most important of the three big battles of Moscow, Stalingrad, and Kursk - had already been won the previous January. The High Command had wanted to send the armies for another push on Moscow, but Hitler overrode them and demanded that they be used to take Stalingrad...and I recommend Anthony Beevor's "
Stalingrad" so you can see how that was doomed from the beginning. Even if the German High Command had gotten their way and got to Moscow first, yes, that was an important logistics hub and would have provided a psychological boost for the Wehrmacht, but it wouldn't have mattered in the end - the factories were in the Urals, and the Soviets would simply have said, "Fine - you've got Moscow. So did Napoleon, and see what good it did him." It was only a matter of time.