Hmmm...IIRC the U-boat wolfpacks were doing quite well at cutting England's supply lines until the US helped out with a bunch of destroyers (50, IIRC), not to mention lots of slapped-together freighters (Liberty ships).
I don't think it was quite as cut-and-dried as you make out, here. Churchill himself counted the war as won when the US entered the war, not before.
And, BTW, whenever production capacity is argued, it seems that only the capacity of the pre-war Reich is counted. How about the added capacity of the conquered territories? Czechoslovakia had quite a military production capacity, as did France.
Comparing a continental Europe subjected to the Nazis, with no war against Russia and a neutral US, to an isolated Britain with it's supply lines undere constant U-boat attack .... seems a much more even proposition to me than you are making out.
Of course, this is all smoke - Hitler was always going to attack Russia, it was at the core of his philosophy. Just saying...