To poke a few holes in your arguments.....
An LHA/LHD would probably not do well with against a well-equipped open ocean threat. While 25-30 AV-8B's might put more iron on target (a little with the ange limitations), they do not have the same supporting aircraft that make up a full Carrier Air Wing. The whole advantage of being closer ot the battle is negated. Also, Harriers are not equipped or could not carry some of the weapons like Harpoon and HARM that would be useful in a sea battle (at the very least, they don't train with them). The Harriers main job is CAS and from what I have seen and heard they are pretty good at it. But an open ocean conflict would stretch the aircraft ot its limits and maybe beyond.
Plus, wouldn't the Marines rather use the LHD/LHA's for amphib operations to push back any enemy threats than play Navy?
You are not completely right about the Brits converting cargo ships into Harrier carriers during the Falklands. They used one container ship, the
Atlantic Conveyer, to transport helicopters and several Harriers down to the two carriers off the Falklands, the
HMS Invincible and
HMS Hermes. The only time the Harriers flew off the
Atlantic Conveyer was to fly to the two carriers. On top of that, the
Atlantic Conveyer was sunk by an Exocet with several of the helos that it brought down still on board. The Brits only had one of the 4 Chinooks after that, the rest were on the bottom of the South Atlantic with the
Atlantic Conveyer. Not a real successful experiment in the end......