It's the losing the FFGs I was getting at. I agree wholeheartedly with you regarding what the flattops would offer. If the flat tops were to happen then I would see them more as a new capability; a DDH per se with ≥ 64 VLS cells etc., that could self escort. Possibly an adjunct to the AWD; not that it's going to happen unless the brown smelly stuff hits the fast rotating object.
If your OCVs have VLS and canister launched missiles while your future LPDs and possibly even your AORs also have as many strategic length cells as will fit without compromising their core roles the light carriers and big deck amphibs can probably get away with a minimal number of cells for defensive missiles only. With distributed lethality any networked ship, sub, aircraft, offshore facility, onshore facility or suitable army capability can contribute missiles' to the offensive and defensive power of a naval task force.
Looking at the cost of the LHDs with their comprehensive combat, command, control and communications facilities, plus the costs of the ANZAC ASMD upgrades verses the cost of the AWDs with their AEGIS systems it is clear that platform size and volume, even power generation and sensors are not as important in platform costs as the type of integrated combat system selected. A big ship with a lot of volume, power generation and cooling, permitting the installation of required weapons, sensors and data links can be much cheaper than an AWD / DDG, or even future cruiser .
So long as you have your command and coordination capabilities within the task group it doesn't (or rather shouldn't) matter if your weapons and sensors are distributed to other ships and aircraft or not. In fact having say your ABMs and land attack missiles on an LPD may be advantageous as this is the ship most likely to be operating in close vicinity to the deployed ARG. Having the LPD and supporting OCVs networked with the ARGs air defence, land and maritime attack missiles only makes more sense. You could have a Camcopter or Firescout from an OCV designate a hostile surface combatant that is then engaged by a missile fired from a HIMARs onshore. You could have incoming tactical missiles aimed at the beach head targeted and engaged by ESSM Block II fired by an OCV just offshore, or by an SM-6 from an LPD, frigate or destroyer.
If everything else can fire tactical and strategic length missiles the flat decks can concentrate on keeping F-35Bs, tiltrotors, helicopters and various UAV /UCAV in the air, not just by launching, recovering and maintaining their own assigned platforms, but by providing deeper level maintenance, support and repairs to the platforms distributed through the task force and ARG. They could even provide a pool of aviation platforms and personnel to be distributed through the taskforce and ARG as required. For example a squadron of Sierras could deploy on the carrier but then individual aircraft could be seconded to OCVs in place of their usual UAV for specific missions. Damaged assets could be returned to the carrier, as slung loads by heavy lift helicopters if required, for repair and return to service that would be impossible any other time. The flat deck could even make use of workshops using state of the art 3D printers and machining centers to manufacture require components for repairs, while their large decks would permit COD flights by tiltrotors carrying other required items and equipment.
Further more the LPDs and LHDs could be configured to swing to carry out similar functions to varying degrees by deploying containerised systems transferred to them after the initial landing / deployment. Alternatively the ADF could investigate if an expeditionary support ship could be a more economical way of conducting this type of support.
The RAN, or more to the point, the commonwealth government, needs its version of Plan Beersheba or Plan Jericho, it needs to move away from the like for like replacements and start looking at the desired effects. OCV was a start but pretty soon sidelined by Smiths lack of vision, then their is the political rejection of carriers (and nuclear power for that matter) where the arguments against and the work arounds required instead of the politically unflavoured option, actually take longer and cost more than doing a proper analysis and then adequately funding the most suitable option would have in the first place.
If the RAN were permitted to embrace distributed lethality and deploy VLS and modular missile systems on OCVs (or better still corvettes or light frigates) then there would be no loss in lethality if some frigates were replaced by carriers'. Once available the carriers could then become a force multiplier through their support of multiple types of air assets including UAV and UCAV, as well as supporting, maintaining, repairing and even replacing helicopters and UAVs throughout the taskforce.