In a sense it is true, but not in the sense we are talking about.
On that question, it is dead clear that the Soviets were, and by a huge margin.
Did US and British troops contribute? Yes. Did P-51s and P-38s help clear the skies of effective German air power? Sure. Would the outcome have been notably different without them? Probably not.
The biggest single setback for Germany, driving deep into original German territory, happened while the US and Britain were pinned down in Belgium and Southern France by a tiny fraction of German assets. Without, the war might have gone on for up to another year, and the Soviets would have ended up owning all of Europe and, probably, Africa. We must be satisfied that that did not happen.
> It only joined the war after Europeans had already killed more than 23 million Germans, and destroyed most of its military.
German military casualties were only 5.3 million by the high estimate. Total German casualties were only 7.4 million by the high estimate - for the whole war. So... I don't know where you get your ideas, but they are objectively very wrong.
That said, the US was far from ready to advance on the German heartland until after the time they were pottering about in Africa. It was a way to look busy.
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.
US had declared Axis powers to be the enemy and then the enemy was defeated. Nobody questions that US was key to winning WWII. It seems impossible that soviets would hold if Nazi Germany was able to send all their resources to eastern front. Even with the help on the western front, soviets held JUST BARELY. And at key moment US troops landed in Italy forcing Hitler to divert his forces that were necessary to win battle of Kursk.
I don't see how you can question that US won the war, it is a fact documented by representatives of states involved in the war signing their capitulation to US.