Disregarding the crewing of Jetconnect, my original point was that fact that Qantas utilisation of 737's is reduced by not flying Tasman services that were previously covered from Australia. Those aircraft now sit idle overnight.
I clearly remember the early starts ex NZ to do 1st flight of the day back to Oz. At the other end of the 'Aus Day' we used to fly Perth/DRW to DPS, CGK, SIN as well as plenty of redeyes domestically. These flights are now operated by additional airframes by different 'entities'.
The additional airframes then need to fly during the day creating overcapacity.
If you think overnighting mainline crews in hotels in NZ is expensive, consider the expense of under utilised airframes & over capacity.