Well, the nub of the problem is that the QE class doesn't have a catapult or arrestor system, and fitting one now would cost about as much as new carrier (we're told).
This means the only fixed wing aircraft that can be used on them are V/STOL aircraft, and that limits the choice to:
Yak-38 - Soviet design, out of production, Uncle Vlad probably won't sell us any.
(Sea) Harrier - 1960's design, out of production.
F-35B - Modern design, very pricey.
So, given that there's only one aircraft that is currently being produced that can actually be used on the QE, that's the one we're going to have to get.
(Whether or not this situation of being stuck with only one choice of plane could have been avoided is a separate rant for a different day)