Except there was no duplication as Jetconnect was already established as a Domestic NZ carrier prior to being put on the Tasman.
There were 4 jets flying domestically in NZ. When Qantas shut down it's NZ domestic operation they transferred those aircraft and crew onto the Tasman and then expanded the operation. The mainline crew who previously operated those routes were transferred to Australian domestic ops with a commensurate drop in hours flown by mainline crew.
And we all know how JC came about don't we? Because mainline Pilots didn't want to fly in NZ.
I'm pretty sure that's not accurate either. Jetconnect was launched in NZ because Ansett NZ had fallen over and QF knew they could get a bunch of crew on lower terms and conditions than mainline pilots then enjoyed.