Your data isn't exactly complete. If you look at the data on flightradar24, it's clear that the plane operating EK434 DXB-BNE-AKL then operates EK419 AKL-SYD-BKK-DXB, which indicates no shiny plane bias in favour of SYD over BNE. But EK412 goes to CHC, so it might in fact be a CHC bias!