I can argue that both ways. Buttressing your point is the fact that altho the US had little military inventory in 1941, that was in a real sense a half truth. In reality, ever since the May 1940 Fall of France the US had been deeply concerned about the war in Europe, and fearful of the effects any fall of Britain (with its famous navy) could have on US security. Consequently the US had been gearing up for military production for a year and a half at the time of Pearl Harbor. That included the well-known infusion of technology from Britain (RADAR, jet engines, and more, including the plans for the Merlin engine) and the manufacture of long-lead-time items like machine tool inventory and factory buildings.At the moment Hitler was declaring war on the US, US military inventory was slim, because the US had been channeling as much military aid is it could muster to Britain. But US military production was just beginning to take off, and over the course of the war it dwarfed that of Germany and Japan.
But if I wanted to argue against the inevitability of US victory, I could point out that the Me 262 jet aircraft would have been available to the Luftwaffe much earlier with more foresight by Goering and Hitler. And as it was, Eisenhower would hardly agreed with the inevitable victory thesis on D-Day, when he carried around a letter announcing the failure of the invasion and taking full responsibility for that failure. It was a close-run thing.
In addition, Churchill worried continually about the possibility that the Germans might tumble to the fact of “Magic.” Without “magic,” the allies would have had a much harder time of it.
What I meant was, if Europe had fallen to Hitler and we had to retreat , it would have only been momentarily. There was no way Hitler could have attacked the USA and in short order, Berlin would have been in ruins, just like Hiroshima and Nagasaki.