Fundamentally this is the same issue as Jet* and Qlink - they operate at a much lower cost base than mainline and so make more money and remain financially viable in the process.
If all Qantas subsidiary employees were paid at mainline rates then the whole group would be bankrupt within a year, and certainly could not compete with the domestic or international competition. The whole world is moving to LCC/value based airline business models, Qantas subsidiaries are currently propping up mainline and delaying the inevitable. Let's be honest, mainline pilots know this - that's why they're fighting so hard for job security clauses in their negotiations, as mainline will soon only exist where it is finacially viable to run a full service legacy airline, only on a handfull of trunk routes both domestically and internationally. Everything else will be done with a subsidiary company at a much lower cost base - Jetconnect doing trans-tasman, Jet* doing price sensitive leisure travel both domesticaly and internationally, and Qlink covering a lot of mainline 737 routes and regional connections in something like a C series jet.