Another interesting point is that much of the British Empire's "warmaking potential" lies in Canada and Australia. Canada, if not outright overrun, would certainly be a major battleground and wouldn't be producing much with the US wrecking Canada's industrial centers. As for Australia, the point has already been well-made re: America's ability to interdict sea lanes.
I think the important point is this: at no point given the stated coalition is the US at risk of being invaded (raids from Canada aside). However, from Day 1 of the war, large parts of the Coalition's periphery are at risk of invasion/interdiction, and after a few years, even their core territory is at risk. Japan would certainly be starved into submission, and while this isn't possible to do to Britain/Europe, after 3-4 years of war the US would easily capable of forcing Japan, Australia, and Canada out of the war, and would have global sea superiority along with heavy bomber superiority - basically, the US would be talking about AWPD-1 on steroids.
Oh, and by the way - we're forgetting about two strong points. China was strongly supported politically by the United States, and would certainly be even more heavily courted. While the US couldn't ship in Lend Lease, at the same time, the IJA would still be tied down in China fighting an unwinnable war.
Even more importantly, don't you think the Soviet Union would be heavily courted by the United States? It would be very easy to make a realpolitik case to Stalin, based both on reality and his fears - ie, after the Coalition beats the United States, what's to stop them from marching East? Historically, every member of the Coalition has invaded Russia - Napoleon, the Crimean War, Russo-Japanese War, and WW1. This would be absolutely crushing to the the Coalition, and almost certainly the most likely outcome. The end of the war would result in Soviet occupation of Central and Western Europe, US domination of the Pacific/Oceania/North America, Indian independence, and the continued existence of Great Britain as little more than a US puppet state.
So, yes, for reasons industrial, political, technological, and military, the US is an unbeatable power in this scenario.