True. But the difficulty is in comparing apples with apples.
Jetstar possibly have the better system for costs, where everything is done from OZ & the aircraft are VH registered.
However, arguably it is better to crew from NZ, as it allows 2 returns per day, with no overnights if operating from a port that has crew based in it. Not that Jetconnect don't do overnights, but that is due to flights being operated into NZ ports that don't have a base.
Productivity is another issue, with NZ allowing a 737-800 to be crewed with only 4 F/A's & also having less restrictive flight & duty time limitations.
I'm would imagine that management have done the numbers & they stack up. But I guess that one can never be too sure in that regard.