The operating carrier pays, but it may also depend on other contractual and partnership agreements between the individual airlines.
Forget about points, which is irrelevant. Think about the 100,000's of QF Silvers, Golds... which are now 2nd class citizens to the influx of QR plats riding on QF metal.
Think about priority boarding lines, which were already a disaster.
Think about ancillary revenue on lost fees from seat selection.
Think about the checked-in baggage weights QF needs to honour as part of oneworld.
Think about QRs new service to Brisbane, which QF had been blocking for since forever.
Do you see a trend?
Think logically.
One must strategically consider why QR offered a match to Velocity members.
Qantas is not kidding -- they NEED Virgin, to survive.