I guess it’s a moot point if it was over weight. All bets would be off on certification requirements
It was 4% overweight by the ATSB's estimation - for which they have presented no details.
the PIC was reasonably light. Lets call the passengers 100 kg ea with 30 kg of bags each. This should still leave over 1300kg for fuel. Google tells me a bit over 100 gph in the cruise = about 320kg/hr = 4 hours range. Even with the new CASA fuel reserves that seems a lot for King Is & back.