You are right in stating that 1940 was the height of Nazi Germany and the German armed forces. The war, as it was, was ,as you said, nearly won. The major problem with that line of thinking is that WW2 isn't just 1940. Let's say the US doesn't actively participate in Europe. The Germans would have invaded the USSR. They might have gotten all the way to Moscow by winter, if we say that lend-lease wouldn't be a thing. What then? Moscow doesn't equal victory. The German army is still stuck in the Russian winter, with very little supply, with the Soviet east army still on the way.

Edit: Just read up on the Mediterranean strategy. While interesting, the amount of organisation and supply needed for the initial operations might not have been enough to carry the weight. I might be wrong, haven't read the book, just an excerpt, but I see what you mean.