It really does show up what many perceive as an issue with Air NZ's fleet. You have 50 seats, 68 seats and then nothing all the way up to 171 seats.
There would be many routes where something around the 100 - 120 seat number would be perfect, but when you have a fleet of ATR's that are a plane built by accountants for accountantss and run on the smell of an oily rag there is no hope of that ever happening.