I believe the parsing intended might have been that the UK and France were "equally exhausted" .. not that the US suffered losses comparable to either.
Even so, the UK lost 3/4 million from 45 million whereas France lost 1.1 million from 39 million .. so that's kind of order of magnitude roughly ballpark from a distance, but France got hit harder.
Correct. The UK and France put together were as exhausted as Germany. And "exhaustion" can't be measured just in body counts. Recall that France had some very serious mutinies around the time of the battle of Verdun.
The "lessons of Versailles" is a dumb phrase. Germany only asked for an Armistice "on the basis of the 14 Points" although Wilson didn't manage to pull that off over England and France's objections.
So we have two counterfactuals, neither of which can be settled:
1) Wilson doesn't propound his 14 Points. Perhaps he loses the election of 1912.
2) He does and the Armistice happens as it actually did, but the Paris Peace Conference declares that the Allies are going to occupy Germany and reshape its government, or maybe Germany is to be dismembered.
It's #2 that this phrase seems to imply. I'd claim that if that happens, no peace treaty is signed at all, similar to the way that the Korean War is technically still going on. The Allies would not have invaded Germany. Russia was already out of the war.
France lost 4.3% of its population. The USA lost 0.1% of its population. I wouldn't call that equally exhausted.