At MEL I don't think it matters which airline one uses, priority baggage never comes out in the first batch for me. At HKG, BKK, SGP & PVG my priority tagged bags always come out within the first dozen bags & I've done all of these airports including MEL one or more times every month since 2004. My conclusion is that there's a conspiracy by the baggage handlers at MEL to deliberately delay priority baggage as spite directed at the high status flyers ie good old Aussie toppling of tall poppies.