QE was designed with STOVL and CATOBAR "potential," and by the time the study into a CATOBAR conversion was made, the lead ship's work had already begun.
There's cost for the procurement of the equipment itself, cost for installation, but also cost for any redesigns and re-engineering that has to be made.
OTOH 076 will be designed from the ground up for EM catapults.
Obviously 076 will be more expensive than an 075, but your comparison is not very useful here either.
Your attempt in explaining the high cost attribution of EMAL solely to the QE acquisition process is not factually supported by public facts as they are well documented. The various UK National Audit reports pertaining to the QE acquisition process issued in 2011 and 2013 and in particular the latter report highlighted the cost blow out with the EMAL option and the subsequent decision to revert to a STVOL based design. Up to that point of time, the UK was in a design phase and the sunk cost identified by the decision was 74 million sterling. It is not a case of EMAL cost blow out to accommodate a design change but rather catapults are expensive by nature especially the EMAL type.
Cats and traps are unique to carriers and these are the capabilities that distinguish it from non-cat design. It is therefore unsurprising they would constitute a significant portion of overall cost. No economies of scale would somehow remove such a high but necessary component cost. IMO, China wants to mirror the capability of the USN with its LHA America class and its STOVL aviation. Lacking such an option, an alternate approach in the form of EMAL being mated to a LHA design is being considered. I think such an approach is fundamentally flawed because the payback on a high investment cost with the EMAL is constrained by a compromised design in the form of a LHA. Said differently, if you want to go for EMAL then go for a mini carrier optimised design to fully leverage the capability arising from your EMAL investment. LHA by design is for amphibious assault with a more aviation centric approach. It is not a carrier centric design.
We know the LHA America gave up a well deck to gain additional aviation storage space. Even with that, the maximum number it can operate with is about 20 F-35Bs. In contrast, the French carrier of around the same tonnage can operate with 30 plus aviation assets.