Ruff,
Noone in their right mind would dismiss the USofA in regards to their role in WW2, essentially it was the manufacturing powerhouse or the western world.
Basically the rest of the players against Germany and Japan were caught flat footed with much of their industrial power either damaged or not up to the requirements of the day, and could do no more than hold the line till the US could get up to steam. I believe the trucks sent but the US to the USSR was a very major contributor to the eventual Russian success.
However why Hitler didn't seal the Mediterrainean to win North Africa after the fall of France shows real lack of vision, imho.
Regards
How was he supposed to "SEAL" the med? The British had the key, - Gibraltar.
3 ways.
1. Make peace with the UK. He tried in an arrogant way, and actually assumed that the Brits would step down and carry on with their lives (thereby lifting their naval embargo on Germany), but they didn't.
2. Beat the British. He tried, but he failed.
3. Get help with Gibraltar. Germany had no chance conquering Gibraltar from the air or sea, however from land if the Fascist leader of Spain, - Franco, - would allow. Hitler did try that as well, but Franco turned out to be quite difficult to deal with. Hitler could not negotiate.
So, he did not lack the vision. The opening of the med was in the mind of the Nazi planners, but it could not be done. (except for one way, - accept Franco's demands and then tell him to STFU somewhat later on, - something not at all abnormal for Hitler, at least later on)
The pont was good though. With a passage through the med and into the Black Sea, Hitler could have struck straight at the underbelly of the USSR, straight into the resources that fed the north, many months earlier, and then being able to turn the defensive logistics into a complete nightmare of transport. Exactly what the German army had to go through itself in 1941-1942.
BTW, the Battle of Gallipoli in 1917 was all about opening up to the Black sea. The Turks were in the way. In 1941 they were neutral, and if anything, pro-axis.