The RAN gave up two Oberon Subs to buy the extra TEN Skyhawks (8 x A4Gs & 2 X TA4Gs all refurbished USN F models). In those days the FAA was valued - what happened? BTW the submariners were not pleased with the loss of 2 of the 8 ordered Oberons earlier.
With the life cycles of submarines, especially their extended maintenance cycles and certification requirements eight boats is the minimum needed for two to be available for deployment, i.e. covering all training and fleet support duties as well.
The level of capability lost the second the Skyhawks, Trackers and Sea Kings could no longer go to sea has still not been replaced. A helicopter with dunking sonar on station is equivalent to a frigate in the screen, no carrier, no Sea Kings, and the RAN is a couple of pseudo frigates down, not just a carrier. Without the Trackers the RAN lost their offensive ASW capability (I should be carful here but others are much better informed to comment than me). Just look what Argentina's Skyhawks did to the RN in the Falklands, the RAN has nothing to match that lost capability to this day.
This is why I have repeatedly suggested that the RAN would be better off procuring a couple (three) DDH or CVH instead of high end frigates to replace the ANZACs. Operating helicopters and UCAVs along there would be a transformational improvement, add F-35B helibourne AEW and perhaps a future ASW tiltrotor the RAN would be unrecognisable.
Its not numbers or money but rather what the money is spent on, or in some cases wasted on. Not replacing the carrier cost more than replacing it would have while reducing capability at the same time. The cheap options pursued by various governments of both shades have nearly always ended up costing us more than doing it right in the first place.
Reducing numbers while taking on more work has seen our ships being run into the ground only to have penny pinching government choose to upgrade the combat power of pretty much shagged platforms meaning we never get value for money from the work done. Alternatively instead of sourcing the appropriate replacement for a required capability billions have been spent on modifying inferior platforms to try (unsuccessfully) fill the gap, i.e. the upgraded FFGs are still in many ways inferior to the retired DDGs and the short fall will not be addressed until the AWDs are commissioned. Also, once tasked to fill the DDGs shoes the FFGs were no longer available to do their job meaning the ANZACs had to be upgraded, at great expense, to fill that gap. At the same time as all this the border protection mission ramped up and the elcheapo, crapo, Armidales were not up to the job and the ANZAC class patrol frigates were off pretending to be FFGs.
Like I said, just because you can look at a list and say there were a dozen destroyers and frigates in the 50s, 60s, 70s, through to today does not mean there has not been serious cuts to capability. Its not about the number of platforms so much as the capability of the whole and if you are missing key supporting capabilities the effectiveness of the whole is reduced and if you lack a sufficient critical mass of platforms and trained personnel you will never be able to do the job at hand.