I don't disagree with this. In fact, that was my point. America had the money, the population, the manufacturing, and the continental US was effectively untouched by the war (yes, there were some very, very minor exceptions). That said, both Germany and England didn't have the available resources and even if the UK was able to build something... it could be in danger of German attack. The Germans were never going to get anywhere close to the Manhattan project, although I do recall in one of the History Channel programs I saw many year ago.... the Japanese launched "explosive balloons" that mostly did little to no harm at all, but one balloon was responsible for one civilian death, and another bomb, apparently hit an electricity transformer that was supplying electricity to the Manhattan Project and I didn't look it up, again, but I think they had backup power, but otherwise, if they didn't, the Japanese could have shockingly caused a mini-nuclear accident when the power was knocked out.
Also, don't forget that the United States was fighting a two front war at the time. So, yes, the Brits were tied down with the Germans in Europe, but America was fighting a very powerful Navy from the Japanese at the same time it was fighting the Nazis in Europe while also developing the Bomb. I'm American, so I'm a little biased, but there really was no other country at the time, even Russia, that could have fought a two front war like that with never having it's continental borders violated. The amazing thing about America during the WWII, was it's ability to PROJECT power. In my estimation, the UK and America, alone could have defeated Germany, Italy, Japan... and Russia. Also, you should note that historians have claimed that the Nazis really were never that close to a bomb. Hitler was not focused on the bomb - it was a longer term project.
