Due to Australias harsh and open environment in the centre or the country particually the deserts Australia needs some light mobile forces, But as they are not likely to encounter dismounted infantry a force is needed with light 76-105mm guns, command, anti tank, anti air, ambulance and APC. This would take a significant load off the coastal defences which currently are expected to cover inland areas aswell
Why? What's there worth protecting?
FYI, Army's 2nd Division (basically all the reserve units) operate the types of capability you suggest we need, except for the 76-105mm guns, anti-air capacity and APC.
What they do have is light motorised capabilities with Perentie styled Land Rover IMV vehicles, to allow the infantry and supporting assets needed to cover the vast distances of this wide Brown land, plus artillery, light recon assets and a range of "direct fire" capabilities.
I agree that 2nd Division should be equipped with capabilities that at least resemble those of the 1st Division, rather than the huge differences that are appearing at present, but it won't happen without massive funding boosts for ADF.
Even if this money magically appeared from somewhere, there are still massive gaps in capability in the regular force to fill first, ie: a medium ranged GBAD capability, an armoured Bridge laying and a mechanised minefield "breaching" capability and other field engineering capabilities we operate only on "paper", a decent IFV for 1 Brigade, the list goes on...