>U.S. and U.K. would not have been able to finish defeating Germany.

It would have either taken much longer but Germany was going to lose its naval and air superiority with or without the Soviets help. It would have turned into a horrible grind but they would have had no effective counter to the US industrial juggernaut and British intelligence as well as facing attacks from the west, north, and south. Couple that with a continuous massive bombing attack to eliminate Germany's manufacturing and transportation infrastructure I don't see how the Allies couldn't have won.

And then US just drops a really big bomb on the Eagle's Nest one sunny August afternoon and Germany most likely surrenders.