No - I will quibble with that. Under our doctrine since 1960s-ish, we can protect a single deployment in one location against everything but ballistic missiles; and depending on proximity to the water and geometry of intercept, we can even do that. I know you are talking about GBAD, but the RAAF has provided the wider IAMD capabilities since the 1960s. They have promised and assured that. Army does point defence and Navy needs a bit more because they operate beyond the coverage of land based fighters.
Yes, we can argue it's been optimistic (although air forces writ large have done pretty good since Vietnam - very few Western SAMs have been shot since Korea, the fighters have pretty much provided that assurance. For a small Defence Force, it made sense to take the RAAF at their word and not buy redundant platforms.
That this isn't feasible against a peer threat (or over-peer) or against modern strike weapons has been realised since we put some harder questions to AFHQ in 2019. That and NHQ's work with DDGs and Standard Missiles, as well as the necessity to conduct our own long range operations has meant less faith in the fighter force. Now we have to grow it.
But fundamentally, a deployed Bde with integral cUAS, point defence eNASAMS, F-35 and E-7 coverage and potentially a DDG nearby can provide significant air defence protection to a single location.