One thing to bear in mind when discussing speed and old ships is that none of our old carriers (including Ark) had anything like the catapult stroke or pendant runout that the QEC fit will have.
However, speed will still be important on recoveries if you have light to moderate wind from astern of your desired MLA as opposed to flying course. Higher ship speed increases the amount of stern wind you can tolerate without having to reverse course off your MLA. As noted before, it isn't about not being able to launch / recover, it's all about operational flexibility - a PITA rather tha show-stopper.
Engines - I think the 30 kts is an assumed WoD for the Mk7 gear rather than ship speed, but am happy to be corrected.
As for the cadre of experience. I remember visiting SFDO/Siskin in around 2000 when doing some early flight decks designs. The WO there had been the last captain of the flight deck on Ark IV. I'm sure we're starting again from scratch here.