There are a few "what ifs" that contributed to the German's failure to defeat the USSR in 1941.
What if they hadn't been delayed in starting Operation Barbarossa? A portion of the German forces that had been earmarked for Barbarossa were sent to the Balkans to bail out the Italians. When they were done there, the soldiers needed to rested and refit, the equipment was worn and needed to go through maintenance overhaul, and the losses needed to be replaced. The Germans got to within sight of Moscow before they were stopped. Would the outcome have been different if Barbarossa had started earlier and the forces that had been diverted to the Balkans had been available for the initial thrust of Barbarossa?
The German military was not highly mechanized and depended to a large part, as the Russian do today, on rail transportation to provide the enormous logistics support network that war requires. German and Soviet railroad gauges were different, so the Germans couldn't travel over the Soviet railroad network without changing the Soviet's 1.520m gauge to the European standard of 1.435m or changing the European standard wheelsets to Soviet standard wheelsets on every car and every engine. You would have expected the thorough Germans to have had a solution to this known problem ready to implement, but they apparently didn't. It takes a lot of transportation capacity to move the huge volumes of POL, food, ammo, repair parts, etc. to where they are need and when they are needed there.
The Soviet KV-1 and T-34 had better armor protection and a more capable gun, the 76.2mm F-32, until the Panzer IVs were up-gunned with the 75mm KwK 40.
Hitler might have done better if he had concentrated more resources on the attack on Moscow and not spread them so thin.
Another one of those coulda, shoulda, woulda if I'd only known scenarios.
