"Whether you can say we're 20 per cent better off, 80 per cent better off, is subject to debate... But the bottom line is, if [the reforms] had the effect of reducing the number of guns that are available to Australians, it is strongly correlated with the gun homicide and suicide deaths on the wane."
"Data from the Australian Institute of Criminology shows the rate of homicide victims dying from a gunshot wound has dropped since the reforms came into force, but not consistently in every year."
"ABS data indicates the rate of assault by firearm causing death has also declined since the reforms, but not in every year."
The only credible argument against gun reform that article gives is that correlation doesn't imply causation, which is of course true. However, that's not an argument against the common sense position that gun reform decreases gun deaths, but an argument against this specific type of study (which OP didn't mention at all).
