I think it start further even back than that.
I go down and watch my mates kids play over here and the level just blows me away- esp in the rep carnivals.
10yr old kids know things I didn't learn till seniors in NZ.
Definitely starts with our coaches being better here in NZ.
We have physically gifted players here in NZ - majority are coached by people with a love for the game but not necessarily the knowledge/experience of the game or even more importantly of how to coach/teach, and so by the time our players reach u20s many don't have a lot of the knowledge that Australians have at the same age.
If something was done to better develop our coaches at all levels in NZ - we would begin to see a real dominance of rugby league in our country.