If you consider the entire North Africa campaign to be "the sidelines" I suppose. I completely disagree with your conclusions, though, because I completely disagree that North Africa was "the sidelines", even with respect to Europe. What were they doing in North Africa? Killing Germans. Was that "selling weapons to Europe", or was it more than that? I claim that it was much more.

Entering the war while Germany and Russia were on the same side would have been fatal, and might even have prevented or delayed their fission.

Staying out long after the split, while Germany and Russia gored one another, was clearly the wiser course. Entering before the Soviets could subdue Germany and overrun western Europe was necessary. But any claim that the US had any sort of primary role in defeating Germany remains nonsense.