You cover a lot of the arguments for the chosen size of carrier, but there are even more, such as:
(1) The larger deck space gives room to rearm and refuel the F-35, conduct take off and landing, and operate helicopters all at the same time (within reasonable constraints) effectively allowing more sorties per aircraft.
(2) The larger ship space allows for adaptation to a wider range of roles, such as LPH, with the potential to operate enough Chinooks to deliver a whole company of marines in one wave.
(3) The F35-B has more than twice the wing area of the Harrier and so needs a bigger deck.
(4) The larger ship has greater potential for adaptation to future aircraft and future roles.
(5) Last, but far from least, it is a more effective deterrent.