In 1930, Germany didn't have the ability to invade and conquer France. In 1935, the United States didn't have the ability to invade and defeat Nazi Germany. We developed the ability, and the Germans would have done the same. They weren't that far behind us on development of the atomic bomb, either.
You may be right about this, but that wasn't the point of that string of posts you've referenced. The poster originally made the following statement:
Any legitimate scholarship and analysis would lead one to the conclusion that WWII had to be fought unless we all wanted to be speaking German and saying "Heil Hitler."
Any statement about what a victorious Germany could have or would have done after World War II is little more than speculation. Even if a compelling case could be made along those lines, it hardly amounts to any legitimate scholarship and analysis leading to the conclusion that Americans would all be "speaking German and saying 'Heil Hitler.'"
Any foreign leader in the middle of the 20th century who had any intention of conquering the United States would have had one huge obstacle to overcome. As a largely agrarian, sparsely-populated nation (in comparison to Western Europe) with a wide array of geographical features and long coastlines on two oceans, and filled with armed citizens -- this country could barely be governed by our own government, let alone an outside invader.