A non stop flight on a widebody is definitely preferable to connecting flights using narrow bodies, the problem is in filling them. Perth - Ho Chi Minh probably wouldn't support a daily A330 but combining pax from other cities into one aircraft in Darwin could make it viable. If the demand is there A330/B787 could even be used on both sectors with flights reverting to A320/B737 in low season. For many Asian destinations you need to transfer in SIN/BKK or HKG anyway. A Darwin hub would give Australia's airlines a more level playing field when competing with Asia's airlines for regional destinations.
It would be ideal if Sydney had been located where Darwin is instead of in NSW. Non stop to London would have been available for years and onward connections to other cities on arrival in Australia would be much easier.
Travel patterns after restrictions are lifted might be very different to last year. Marginal direct routes could be dropped and a transfer needed instead. The B787 and A320NEO could start replacing B777 and A330s, A380/B747 gone from all but the busiest routes. Reduced frequencies. Definitely fewer pax up the front end paying premium fares.
Eventually travel will return to 2019 levels but it will take time and there will be many changes in the short term.