Why two large carriers led to LHD thinking

Why not build a third Queen Elizabeth-class carrier, and could smaller vessels help?

The service was limited to two large carriers, so ski-ramp LHDs are presented as a more flexible backup aviation option.

The discussion frames the problem as resilience rather than simply carrier numbers. The Royal Navy was authorised to build two large carriers, so it maximised the capability of each hull even though only one might normally be available. Ski-ramp landing helicopter docks could operate F-35Bs in an emergency while still performing amphibious and helicopter-assault duties. That common aircraft and overlapping ship capability would give a medium-sized navy more usable flight decks without supporting a separate carrier air group.