That's only partially correct. I have flown QF9 and QF10 multiple times on the A380, the last of which was my last international trip before the pandemic with upgrades to first class both ways. QF9 and QF10 flew on the A380 via DXB in the final years it was using the A380. It did switch permanently to the Dreamliner when it switched to going via Perth, but it did use the A380 and the 747 before that.
Back when the A380 was used for QF9 and QF10 some SYD based fliers chose to fly on it because they preferred the timings, perceived a higher chance of an upgrade or to get additional SCs for a more indirect route.
Even when the PER flights started QF still flew a separate A380 to SIN from MEL (although there was a several hour gap after that before the onwards flight to LHR on QF2) as well as an A330 flight (that was timed better to link up with QF2), so there was still the opportunity to fly the A380 to LHR from MEL without going via SYD.