Some thoughts from an interested observer. I had a daughter in the 18's GF (played against both SA teams) while I saw some of the 16's girls and coached in the 14's.
Chemistry is absolutely the responsibility of the coach, HOWEVER, you can start behind the 8-ball with the personalities you have (often imposed up on you and based on developing 2 fairly even teams instead of the best combination for that team). I was lucky enough to have a great group of kids this year and could build from there.
Secondly, you get outstanding age groups from time to time, and equally, down years. The NSW Waratahs 18's team this year got a job lot of athleticism, and when up against a less than athletic group from SA, the skill differences were exacerbated. As the kids get older, these fitness differences tend to become greater. At 14's, the fitness differences are not so great, and so the skill differences not so obvious.
While the NSW 18's age group isn't outstanding by any means (though they did finish with a silver medal at Nationals 2 years ago), they are capable and fit, whereas the SA group are perhaps a little below the usual level. At 16's a couple of outstanding players brings that SA age group up enormously while the NSW group at least struggled all week with injury, illness and internal division (which incidentally they brought into camp with them).
The other issue is where the various teams are at in their preparation. I don't know about SA, but I know the Vics are well into a comprehensive preparation when they come away. NSW have four sessions before the tournament starts ad take a very developmental approach, particularly with the 14's.
I don't think the SA 18's where as bad as some believe, but they look bad against the two 16's teams that played each other in the GF. Last time I checked the score one of the 16's teams was kicking the other so does that make the second-placed team a bad team?
We sometimes forget that these athletes, as maturely as they play at times, are still just kids and prone to all the fluctuations of teenagerdom that most 12,13,14 and 15 year olds suffer.