The Australians aren't that weak as a group of skaters. Both Kerry and Craine made the cut for the FS at both Olympics and Worlds, and their Pairs team made the cut at Worlds. OTOH, Canadian lady #3 didn't make the FS at either Oly or Worlds, and even more shocking, Canadian #3 Pairs and #2 Man didn't make the cut at Worlds.
The Australians placed 18th (men), 17th (ladies), 16th (pairs), and 30th (dance) . While I hate calling skaters/countries "weak", those results show they aren't strong in any particular discipline (yet).
But more importantly, someone placing higher than another skater doesn't automatically make that country's group of skaters better as a whole, or a lower-placing country "weak" as a whole.The top Australian man beat the top Chinese man (as did the top Uzbek, Latvian, Italian, French, and Swedish man). So is it logical to extrapolate that Australia, Uzbekistan, Latvia, Italy, France and Sweden are all better at men's figure skating than China based on comparative results from the most recent Worlds, since the best of those countries beat the best of China? Jin (the Chinese #1, in terms of World ranking) came 19th, so does that mean Yan (had he competed) wouldn't have done any better, being the next best ranked Chinese man?
Yes, Nam (a former 5th place finisher at Worlds, mind you) happened to not make the cut. Back in 2010, Nobunari Oda (who was 2nd at Japan Nationals 2010, a season where he won both GPs and the GPF silver) didn't make the FS cut at Worlds in 2010 placing 28th. So does that 28th placement define the ability the entire Japanese men's field? Or even Oda's own ability? Heck no. Just like the 25th placement is obviously not Nam at his best, and it's futile suggesting it is -- his skate at 4CC just prior to Worlds got 84 points compared to his 67 at Worlds, a score which would have put him 10th after the SP (his ISU season's best would have put him 8th after the SP at Worlds).
As for the ladies' Canadian #3 (25th), that result is not representative of the rest of the Canadian ladies' field - many of them could have made the cut (Chartrand's and Pineault's SPs at Four Continents 2018 would have made the cut at Worlds, for example). Even Austman's skate from the Olympics would have had her make the SP cut at Worlds. So you can't extrapolate like that and say it represents the whole field of that country, let alone that skater's own ability. The same way that the #3 Russian lady Konstantinova coming 19th doesn't mean that the rest of the Russian ladies field would have placed no better than 19th themselves.