I just pointed out that American LHA's/LHD's carry 6 STOVL Aircaft. As do Spanish Navy LHD's.........
The one and only Spanish LHD (
not "LHD's" [sic]), when she's finished building & is in service, will not carry 6 STOVL aircraft. She'll carry none most of the time, & sometimes, when reconfigured as an aircraft carrier, with her dock sealed (so not able to function as an LHD) will carry as many as needed, which if she's actually called on to fight, would probably be as many as they can cram aboard, i.e. about 12 in the hangar & a few parked on deck.
The US navy & its practices are not relevant to either Spain or Australia in this context. The USN has ten LHAs & LHDs, each of which is 50% larger than the BPE. It also has 11 aircraft carriers, & 9 LPDs. You cannot view the air group of each LHA/LHD in isolation, divorced from the context provided by the 29 other ships.
Spain, on the other hand has
one carrier, & will have
one LHD, only one of which will operate STOVL aircraft at any given time, & just two LPDs. That places their operations in a very different context. The two LPDs will be refitted, one at a time, when the carrier is active. Therefore, the normal available number of ships will be three out of Spains four. The LHD will either be one of only two operational amphibious ships, with a carrier also operational, or it will be the only operational carrier, but both the LPDs will be available. When the carrier is operating, all the fighters will be on her, & the LHD will need all its amphibious capability, because usually only one LPD will be operating. When the carrier is in refit, the LHD will function as a dedicated carrier. At no time will there be either the need, or the spare aircraft, to operate any off the LHD.
Australia is building only two LHDs. Some of the time, only one will be available. Squeezing a handful of F-35B on it would compromise its amphibious function, & those few fighters would be castrated by the LHDs inability to support them properly.