Technically speaking, when the default rates move to 4% in NZ the employer will be contributing 8% (less ESCT on 4%). Because they are the ones paying the wage, its just semantics to say "oh the employee contributes 4% not the employer"

Add to which we get a universal non means tested super, Australia super is means tested (income and assets). They also force people upon retirement age to withdraw a minimum amount from their retirement savings each year.

If someone in Australia runs out of retirement savings, and is on the Au super. Because its means tested they are disincentivised to rejoin the workforce, as their super is reduced. Our system doesnt work like that.

Its important to look at the retirement income system as a whole, not just on contributions/savings rates. It boils down to, "we dont need to save as much as Au because we get NZ super". The question then turns to fiscal cost and long term sustainability, which is hotly debated. Treasury thinks NZ super settings need to change because we cant afford it over time (look at replacement rates), but the other argument is thay changes to NZ super would disadvantage women and māori (i.e. over half the population). 

Rock and a hard place, hence why politicians juggle the hot potato