...and do those sorts of distances prove any obstacle at all to a fully embarked Chinese nuclear powered carrier?
China is rapidly developing that capability - the Type 004.
Or to a nuclear powered submarine?
Their boats might be noisy now... how about in a decade?
Or to a large unmanned, underwater vehicle?
Cheaper and quicker to develop than anything manned.
Following the logic of your argument, absent ICBMs, Australia shouldn't need to worry about a military threat from China because we're simply too far away, and the Indonesians and others are an obstacle?
In the medium to long term, the threat clearly is not just focused north of Indonesia, or PNG for that matter, or predicated on the Chinese having large, well developed bases in Thailand or the South West Pacific to operate from.
Anyone who believes Chinese assertions that they are simply defending to the Nine Dash Line or their immediate neighbours is naive in my view.
Every sign points towards them wanting long term to hold at threat a huge arc from the Bay of Bengal, down as far as the Coral Sea, and possibly even out as far as the mid Pacific.