Go to KGI. It's fine the way it is. Long enough and the 789 RNP AR capable. Simple.
Not so simple if you actually had to go there after a long-haul flight from LHR:
- Limited runway length.
- Tiny apron with limited parking for large aircraft. What if several other A320/737 type aircraft diverted there before you?
- No RFF.
- No CIQ. All passengers & crew would have to remain on board the aircraft and wait for a relief crew to arrive to fly the aircraft back to Perth. That could mean a long wait on the ground for passengers and crew who have already been on the aircraft for over 17 hours.