As i said earlier, give me any day a leader that will kill me for my political ideas rather than a leader that will kill me for my birth circumstances. I can always shut up about the politics, but i cannot change my genetics nor my disabilities.
I am not certain that they could have defeated the soviets, but they certainly could have made it better: taking Moscow and retaining Stalingrad, and reaching the Caucasian oil. They could have forced a peace treaty with a purely Siberian USSR... but they would have still lost in the end, because while they would be busy building up strength for a successful Sea Lion (it would take years), the Soviets would be building up strength to restart the war.And on the debate of Soviets defeating Germany... Well, if the Germans started operation Barbarossa when they wanted, around 2-3 month earlier they would have destroyed the Soviets.
In any case, Germany was doomed from the moment that Britain and France decided to actually honor their word to Poland and declare war on Germany. Hitler really wasn't expecting them to, not until Poland was occupied. He was also counting on the possibility that since the Soviets had invaded Poland too, they would aquiesce to a German-controlled Poland as lesser evil.
But that failed to happen, and the British and French still kept their war declarations after the Soviets invaded. Then Hitler was hoping to hit them hard enough as to force a not-too-harsh surrender: the conquest of Norway and Belgium. That still didn't sent them to the negotiation table. Then Hitler hoped that striking France hard enough would scare the British, and get a peace with the Brits and a surrender from France. That didn't happen, and France only surrendered when completely overrun. Then Hitler STILL thought he could force Britain into peace talks by bombing southern England and threatening to do a (completely impossible at the time) amphibian invasion. And that didn't happen.
Why was Hitler hoping and hoping? Because he didn't want a war in the West in the first place. In the Nazi ideology, the only war is the war in the East, against the weaker eastern countries and Russia, to convert them into German Lebensraum. To convert the natives of those lands into serfs for German landowners who would live a ruralized life.
If any of those expectations had happened, if France and Britain had agreed to sign a peace treaty with the Nazis (unlikely, they knew in the long run they would win, because they outproduced Germany), if Germany could have started the war with the USSR during 1940 (when the industrial advantage was still German), history might have gone differently.