> I believe that involves some creative accounting where all tourism to royal-adjacent properties and the surrounding areas is attributed entirely to those properties still being owned by a living monarch rather than the state

That argument is a tricky one (as you point out). The French palaces have a fair few visitors and there are no living royals to block access. The family don’t need to be in the castle.

It’s ludicrous as they are also my royal family - and I’m in New Zealand.