Actually, the opening of the Soviet archives makes it unclear whether the invasion of the USSR was a mistake. Not doing it a month or two earlier, not providing winter supplies to the troops, splitting forces between the drive on Moscow and the drive on the Caucus oil fields, not falling back to regroup at Stalingrad, those were mistakes.
We now know that Stalin planned to abrogate the Molotov-Ribbentrop Pact by launching an attack along the Carpathian Mountains with specially trained mountain divisions, thereby cutting off the Reich from its only source of non-Soviet oil, but Hitler struck first. Had Hitler not invaded the USSR, the war would have been over very quickly, with Stalin dictating the terms, rather than Stalin, Churchill and Roosevelt jointly.
It was well inside the Russian mentality that Moscow could be sacked by an enemy. Napoleon did it. But they don’t associate that with the nation collapsing. They would have simply moved east and fought on, like moving factories. So focusing on Moscow, etc would have not changed the outcome, unless of course, we stopped lend lease. (which could have happened had they collapsed)
Also, interestingly, Hitler never intended to take all of Russia. He was intending to go to about the Urals and never set foot in Siberia, believing nothing could ever be assembled there that would threaten him. Essentially he wanted the European half of the USSR.
They actually had planned to attach Russia sooner but had to wait and help the inept Italians with their invasion of Greece. This wasted a precious few months.