Hitler wasn't able to keep up producing the supply of synthetic oil he needed to run his military. He invaded Russia to take control of Russia's natural resources. Lebenstraum in Russia was the least on his mind at that time in the war. He had all the other countries he'd invaded for that plan. And he never would have conquered all of Russia to gain access to the whole country anyway. He chose poorly to begin with, and then he split his army, which was his downfall.
Hitler should have employed a “Divide and Conquer” strategy. Promise the Ukrainians autonomy and to be “under German protection” in exchange for helping the Nazis fight the Soviets.