Respectfully, I believe you have confused "new" with "state of the art". China is likely using batteries because their battery production is subsidized, Australia's trading partner is China so basically equivalent.

Perhaps a bad analogy, but it seems these battery systems attempt to stabilize by "pushing", whereas spinning mass can also work through "dragging" the phase. So eventually, you will have just a few rotating masses setting the freq and phase, with more and more systems tracking that and pushing, which seems like a recipe for chaotic equilibrium.