obviously any NZ airline can fly within Australia without restriction. Don't even think they have to have much interaction with CASA.
Plenty of routes that aren't flown.
With much lower costs, a NZ airline, can operate thinner OZ domestic routes profitably, that an Australian airline can't make profitable.
Crazy but true.
It's like Australia paying the Kiwis something like $21 million a year to dump their wine in OZ, whereas the OZ winemaker gets SFA & has to pay tax on their wine.