Why a one-carrier fleet loses availability

Would the Royal Navy be better off with one larger conventional CATOBAR carrier instead of two Queen Elizabeth-class carriers?

No. Two carriers preserve availability through maintenance cycles, while one carrier is often unavailable and a conventional large hull sacrifices volume to fuel.

France's one-carrier model is a poor availability model for Britain despite the prestige of retaining a CATOBAR carrier. A carrier must rotate through maintenance and its machinery is heavily worn by sustained operations, so one hull can leave a navy without a carrier for long periods. Keeping one ship continually deployed also damages crew retention even when people can endure the immediate tempo. A conventional ship with a larger air group gives up hull volume to fuel as well, compounding the availability trade-off.