Slow MPAs like Poseidon and Triton can get shot down 1000 km away by J-15 combat air patrols.

Conventional subs can't catch fast moving destroyers and carriers in the open ocean. They need to ambush or attack in constrained waters. Moving in the open ocean opens them up to getting sunk by frigates with towed arrays or ASW helicopters.

Air force is too short legged to really threaten oceanic fleets without tankers. tankers then limit the number of sorties. There's only 7 Australian tankers.

Standard JASSM doesn't have an antiship seeker. It hits only stationary targets. LRASM is the anti ship version which is only US deployed. JASSM is also slow and short legged with only 370 km range. Harpoons are even shorter legged.

Meanwhile PLAN YJ-12s are near hypersonic and have 400+ km range. YJ-18 is slower but has 500+ km range. PLAN can also hit Australian political, economic and military targets from 1500+ km out with ship launched CJ-10s.