"What good are these ships if we cannot achieve at least a measure of air superiority?" Well they can do their job while someone else takes care of AD. Why do we have to achieve that air superiority when Allies can do it for us, perhaps with land based AD assets? We can't do everything, and the politicos have decided that we won't do autonomous ops, without allied support.
AD may well be required to allow ops "where there is an air threat considered to have the potential to saturate or evade ship based defences", but that's a) rare, and b) something which will often be within range of land based AD. And who is to say that it has to be provided by the UK, and not by an ally during this six year gap. We can't do everything, and the politicos have decided that we won't do autonomous ops, without allied support.