The reason flights are cheaper from Oz doesn’t really have much to do with hubs. It’s everything do to with their market being far more competitive and Air NZ having to offer cheaper pricing to attract passengers. If you are booking a flight ex Australia you should be able to arrange a stopover of more than 24 hours in Auckland which will mean your bags can be short checked and there is then no need to fly the final leg back to Australia.
I read of one person on another airline doing this and complaining because despite the layover he didn’t get his bags back. The airline had kept them to prevent this short checking so if I were flying to Oz to then head to the US I’d fly the whole lot as painful as the extra time would be, but if the price is right I’ll consider it!