Why US and Japanese fleets differed from the Royal Navy

Were the US and Japanese navies designing to refight World War I while the Royal Navy prepared for future warfare?

Partly, but the deeper difference was strategic: the United States and Japan focused on each other in the Pacific, while Britain had to cover several theaters and missions simultaneously.

There is an element of the United States and Japan preparing to refight familiar battle-fleet problems, but strategic geography matters more than imitation alone. Both navies expected a Pacific contest centered on one another and could concentrate design priorities accordingly. Britain had to hold the Far East, fight in the Mediterranean, protect the North Atlantic, and meet other imperial commitments. Those different mission sets forced different fleet structures and made the Royal Navy plan for a broader range of warfare than a single decisive Pacific death match.