So why has nobody done that? Why do most navies that build amphibious ships think it’s worth having a couple of different types, e.g. an LHD & a cheaper (& usually smaller) LPD or LSD?

Might it be because a high/low mix can provide more flexibility? Because having more ships is more flexible, enabling one to send a basic LSD when that’s all that’s needed, & save the more expensive LHDs for the tasks only they can do?

exactly. The UK does not need 6 full on LPDs of the Albion class. It needs a couple for high end ops and the much simpler bay class for smaller ops and everyday taskings. They have proved very useful, dock, good sized flight deck, loads of cargo space and four of them for much less than full spec ships. its a model that should be pursued across all types of ships me thinks (hopefully so with C1-3).

As for my comment about the various carriers, my point is that the Euro harrier stuff is more akin to a US LHDs and really can’t be listed in comparison to a CVN. Only QEs and CDG can. it underlines that even if they had 9 ships the USN has massive advantage over everyone else.