Troo believer:
I guess you missed the bit where I said "Not so simple if you actually had to go there".
Not a large aircraft? Well I guess that's debatable. It's a darn sight larger than the B738s and F100s that regularly use the place. It's also bigger than the B763, the largest type for which there are parking bays available on the apron.
Cross that bridge when you come to it? So what do you do when you arrive there in your B789 and find the apron is already full? Park on the runway and block the entire airport? Jeez, you'd be popular.
Runway heaps long enough? At 2,000m try barely long enough.
Don't need CIQ? No, you don't, but all pax and crew would have to remain onboard until the aircraft could be flown out. That would mean waiting for a relief crew to arrive from Perth, because the crew that flew it in would be out of hours. That could be a long time, depending on the time of day, especially if flights can't get out of Perth.
Don't require RFF? Maybe not under Australian rules, but only because Australia has filed a variation to ICAO's Annex 14 requirements, which most certainly do require RFF. International operators such as CX are not allowed to plan airports such as Kalgoorlie or Learmonth as alternates because those airport have no RFF.
Sure, you could legally plan Kalgoorlie as an alternate for Perth (although I'd be interested to hear CASA's views), but the practicalities of actually going there would not be anywhere near as simple as you suggest.