I am not sure you can compare apples for apples here. Air NZ does enjoy a less than competitive landscape into / out of New Zealand compared to Qantas into / out of Australia. There are some 60 + airlines flying into / out of Australia today. Around 10 just from China alone. 31 airlines into / out of New Zealand. Qantas has code share arrangements on many markets in response to demand (thin routes). Some markets are pretty saturated these days. Why operate the market at a loss with your own metal if you can make money with a code share?
Qantas would need to serve new markets. It isn't that necessarily easy depending on bilaterals (if rigid), equipment type and availability etc. It does not make sense to redeploy capacity away from one market if it is achieving strong unit revenue there...