Sea control in choke points outside of Australia's waters was an OPC / Corvette role, hence their NSSM/ESSM, Harpoon and Penguin equipped Super Sea Sprites. It was seen to be the minimum required to survive in lower threat areas outside of Australian waters with the upgraded (for and with?) ANZACs and FFG/DDG replacement class of 8-9 high end air defence frigates (think New Threat Upgrade standard rather than AEGIS) dealt with the higher threat zones.
This plan lasted from the Dibb review and subsequent white paper, until the early/mid 90s with the recession we had to have / Keating PMship, followed by the Howard government first and second term cuts.
Realistically 8 SSGs, 9 DDG/FFG, 8 PF (ANZACs) and 8-12 Corvettes, 16 upgraded Seahawks (Penguin etc.) and 27 Super Sea Sprites was probably unaffordable, but it was seen and the minimum needed to control our regional sea lanes. Back then less sophisticated platforms were good enough and greater numbers were more affordable, now threats make the minimum necessary capability much more expensive, hence reduced numbers.
Before anyone arcs up about crew numbers, just remember the DDGs had crews over 330, FFGs had nominal crews of 180, but were deploying with 200, and the River class DEs had 250 crew members, even the O boats had 67 from memory. When these plans were made it was assumed that the RAN manpower would remain about the same, it would just be spread over more hulls. When plans were delayed, projects deferred or cancelled, and economies made, manpower, particularly among technical sailors and engineers, reduced. By the time the money from the mining constructionc boom started flowing into the government's coffers, the RANs engineering capability had been gutted, ship building had gone over a decade (two government's and three PMs) without orders for any new warships and, with the last ANZACs and Collins finished construction and in final outfit, about to enter an industry destroying shipbuilding black hole.
It could be argued the billions it cost to remediate the loss of RAN engineering capability and shipbuilding skill, could have quite easily paid the wages of retaining the extra personnel as well as building the extra hulls. The Coles, Rizzo and other reports, as well as the current ship building plan seem to confirm that at least the current government realises the 90s and 2000s were full of bad planning, a lack of foresight and missed opportunities.