Why later British battlecruisers were still likely

Would another British battlecruiser class have been inevitable without the First World War?

Yes; global presence and economic-warfare needs still favored a fast capital-ship branch alongside battleships.

The Royal Navy might move from the Queen Elizabeth and R classes toward an Admiral-like design even without wartime interruption. These ships sit on a spectrum between the earlier two-word battle cruiser, the later integrated battlecruiser concept, and the fast battleship. Their speed and reach particularly suited Britain's need to defend and attack maritime trade worldwide, a requirement less compelling for continental powers.