So, if America's enemies had been deterred for a while, wouldn't they have improved logistically and technologically even more quickly? That is to say, the sudden, overwhelming entry against already over-extended foes was arguably more effective than gradual escalation.
But there were definite limits to the size German armies and their could achieve could achieve, and the U.S. 's limits were far and above those; we kept both the allies and the Soviets as well as ourselves in the war via our production capacity, our own fuel and mineral resources, and more than enough skilled manpower to out-produce any possible combination of enemies, and we fought on three fronts as well at the same time. They would have had to back down at some point, on all fronts. If we had entered the war earlier, we would suffered fewer losses and the war two years shorter.