Australia is an island, albeit one of continental size, but an island nevertheless. Having the army focus on the littoral environment makes absolute sense. No the Army isn't the USMC
BUT it needs to focus on its amphibious capabilities. You aren't going to be fighting in the western desert or the wide open plains of Europe, but on islands, and in archipelagoes which, if you look at map, close to you and numerous. A division / brigade / regiment of armour and mechanised troops is no good to you if you can't get it to where it's needed. Last time I looked M1 Abrams and the IFVs under consideration can't float or fly. I have said for yonks that the upcoming war in the Indo Pacific will be much like the Pacific War of WW2. The Australian Army, amongst others, is not structured our outfitted to fight such a war.
The whole focus of the DSR is the Indo Pacific and focusing the ADF towards the threats, real and potential, against Australia. It says:
"Our Alliance partner, the United States, is no longer the unipolar leader of the Indo-Pacific. The region has seen the return of major power strategic competition, the intensity of which should be seen as the defining feature of our region and time. As a consequence, for the first time in 80 years, we must go back to fundamentals, to take a first-principles approach as to how we manage and seek to avoid the highest level of strategic risk we now face as a nation: the prospect of major conflict in the region that directly threatens our national interest." P.17. Emphasis mine.
Let's look at that: "...
for the first time in 80 years, we must go back to fundamentals ..." That is the operative term. The current Defence of Australia strategy is no longer fit for purpose. So things have to change. It says later:
"1.7 As a result of this new strategic reality, our view is that this is not ‘just another Defence review’ that will shuffle available resources, or tweak the balance of the ADF. This Review, in conjunction with the acquisition of conventionally-armed, nuclear-powered submarines, will reshape the force structure, posture and capability of Defence for coming decades – and necessarily so." P.24. Emphasis mine.
This isn't a cost cutting exercise as some claim but a complete restructure of Australian defence from the ground up. You need to look at the whole review within the context of that. They intend to move the ADF to a position where it can provide for the defence of Australian people and their way of life. Because of this needs and capabilities change.