Facts....?

No. This is, as you say, entirely conjectural. Churchill's long-standing strategy to confront a resurgent Germany could be summed up in two words: United States.

Britain alone was not in danger of being conquered by Germany—witness her victory in the Battle of Britain—along with possession of the world's largest navy & a vast overseas empire. Yet she could not effectively fight Germany w/o the US. FDR skillfully brought an understandably reluctant nation into the European war. Yes, Hitler declared war against the US, but that came from frustration at fighting an undeclared naval war in the North Atlantic. Once the destroyers-for-bases deal went through the US could no longer in any be considered neutral.

True, Churchill would not admit the Empire was closing shop. I agree, he saw the writing on the wall. But there's no evidence he blamed FDR. Britain's post-war impoverishment was due more to Congressional insistence on repayment for Lend-Lease than any particular chief executive.

Britain wasn't only a supplicant, either. Her intelligence & code breaking contributions were essential tools to gaining mastery over Germany. The Tizard Mission, which brought British breakthroughs in micro-wave radar to the US, has been called the most valuable product ever carried into the New World. Her contributions to the Manhattan Project were also essential.

You've heard the phrase: British brains, American brawn & Russian blood.

I'm not prepared to argue the British Empire, good or bad, but it had a good run as empires go. In committing all to fight Nazism it set the stage for decline with a degree of honor seldom seen in imperial history.