It's really a horses for courses thing which is of course an unhelpful non-answer. But it's all highly dependent on what you want from your career and what moves you are willing to make within it and geographically in life.
If your ultimate desire is to get into Air NZ then taking the offer as a turboprop FO is the way to go. There's a fair amount of hand-wringing about the current recruitment pathways which you've probably read so I won't re-hash it here. But I will say, perhaps unhelpfully, nothing in aviation is static.
In saying that I feel long term if you don't want to be moving around employers then Air NZ is probably not the worst place to be. Starting as a turboprop FO means you a directly employed whereas with Qantaslink you are not.
From an outsider perspective the industrial landscape in Australia seems pretty harsh and the future seems like it could be turbulent, whereas it's fairly straight forward in NZ and relatively stable although I'm sure some will disagree.
You are right that NZ can be very boring but if you have family and friends here and want to start a family of your own then sometimes boring isn't too bad. That said I'm very keen for Auckland to grow up a bit more and become a proper city.