Wonder if the MH captain was influenced in his questioning of the initial route by the fact that an ANZ B787 going to Singapore took off just before him and went on the "northerly" route heading for overhead Brisbane?
The MAS flew over the top of Singapore just as the ANZ landed there. Flight times on the two different routes ex Auckland were therefore comparable. ANZ went overhead Brisbane and Darwin; MAS went overhead Sydney and Alice Springs.
Information from FR24 replay.