Get a grip on reality for a second. Rebuilt MEL? THey've just expanded international, the connection thing works smoothly, what on earth does competition in duty free have to do with rebuilding the airport? Airport operators I am sure charge handsomely for the monopoly to operate DF outlets. At SIN (not sure about HKG) you will also find that in the "traditional" DF stuff - alcohol, perfumes and tobacco - there is also no competition (within the airport) - the competition is really between airports (yes with MEL, SYD, HKG, BKK, KUL etc ...).
Australia's airports are fit for purpose. Even SYD would be OK if they just build a SIN/KUL/HKG style people mover driverless trains that ran every few minutes between INTL and domestic.
The airports are basically end of the line airports (other than for domestic transfers) that are not competing with other nearby airports (in other countries) for hub traffic. SIN airport, economically is extremely important to the city-states economy, and not just as infrastructure to support the SIN economy, but as an income generator in its own right. Similarly the geographical location of KUL, BKK, HKG (and now DXB and AUH) all see them competing with each other and SIN for important and valuable connecting traffic. So to expect SYD or MEL to be anything like those - forget it - Also our airports also don't come with a sense of national pride that those in the more developing countries do.
If you want to see how painful airports can be, I'm sure there's a few examples in the US.