Regarding the ski jump, allegedly it is an integral part of the hull design engineering. At least that’s what the Aussies said in denying that they were going to buy F-35Bs to go along with their As and use it as a true light carrier.
But it will certainly allow the Turks and Aussies to operate F-35s, if they choose to do so at some point down the road.
It's more a matter that changing it is more trouble than it's worth - cost savings and performance improvement would be very marginal.
And it does keep options for the future - both in terms of operating our own STOVL aircraft in the future (which would, at present, of course, mean purchasing F-35Bs) or as additional decks for allied ships we're operating alongside.