I think the Germans lost the war by failing to take Gibraltar in 1941 and also failing to take Malta and effectively blockading Alexandria, which would have contained the British from the Mediterranean and boosted the Axis. Therefore, Barbarossa was a desperate "way out" of stalemate in the West instead of an opportunity to secure Germany's back door, and hopefully also to gain directly the resources of an unreliable and reluctant Soviet partner.
Capturing the BEF at Dunkirk might have ended the war, but it is unlikely that the Germans could have done that because they still thought they had the French to defeat, and the generals wanted to play it safe and halt the panzers, to which Hitler agreed.
Also, I agree that Stalin/Molotov overplayed the Soviet hand in 1941 with Hitler, and he resolved to end that uneasy partnership and eliminate the burgeoning Russian threat.
Germany probably would have still lost the war without American involvement. But I do not see how Germany could have still won the war after Pearl Harbor and American involvement. At best, she could have not LOST the war if she had developed the atomic bomb in time as a diplomatic deterrent.
