I disagree on the premise that the the main role of an air group should be anti surface. The RAN is going to operate throughout archipelagic sea lanes and into the Pacific or Indian oceans. In all scenario's but particularly in the 1960's / 1970's this will be beyond the range of friend land based fighter aircraft. The ability to have organic fixed wing to be able to protect the fleet is critical in this situation. When we take into consideration the low probability of kill of missiles during these decades.
Air defence is vital, but with an extremely limited air group one has to go with what will make the greatest difference against the most likely adversary, especially during the 1960s when missile warfare and fast attack craft was coming of age.
In such circumstances, the ability to denude a likely enemy fleet of offensive assets, or at the very least prevent an attack on your own ships or commercial shipping, would've been achievable. Such aircraft would also be able to tackle any incursions by reconnaissance/bomber aircraft.
Sacrificing significant air-ground/range/loiter abilities for the sake of having the same number of slightly better fighter aircraft, which would in any case be aboard in tiny numbers unable to tackle a concerted air attack, would not make as much sense.
As mentioned previously, A4s were hardly slug-a-beds when it came to air combat either and, as you mention, the missiles of the day were rather poor, most especially air-to-air ones, so further reducing the superiority of a dedicated fighter aircraft as it'd come down to a (subsonic) gun fight.
With a bigger carrier there are options to cater for more scenarios, ranging all the way up to the US super carriers that single-handedly carry sufficient aircraft and munitions to overpower probably 50% of the world's air forces.
Had the RAN operate a larger carrier (Clemenceau to Ark Royal sized or so) it could've had a more powerful and mixed aircraft complement, such as F8s, A7 Corsairs and/or Skyhawk, but all that would've cost far more money and manpower, and come at the detriment of the rest of the RAN or RAAF.