You'd need to move the Australian limits down ~30% to have a similar tax system to Australia. Australia's median wage is ~30% higher than NZ so they are able to get the tax take they need with higher thresholds.
Frankly that seems like less of an issue - but there would be an interesting discussion to have about how a lower/zero % threshold plays nicely with WFFTC. It's probably something best done sooner rather than later.
As for National's Budget snaffu... it would be funny if it wasn't so sad.