I don't know what went on but Australia are slowly being updated by media.
My comment is more in general, if police can use their authority or use lethal force (if appropriate ) they might have acted sooner.
I feel for the nut jobs family, but he was always going to be taken down. Sadly he is not here to answer for his crime but he killed. Innocent people before he was stopped that's a dozen families left to suffer.
They're fully authorized to use lethal force and "go to the gun" as they say in an active shooter situation. They didn't and nobody can figure out why. 911 calls were being made and shots were being fired and they apparently did nothing for at least the length of a sitcom. They'll say that the officers were following orders being given at the moment or following some sort of protocol but it isn't going to wash with most folks. If someone is in a building shooting kids you just rush in. Break down doors. Take a bullet or six if you have to. There are worse ways and reasons for dying.
Frankly I think it's better when these monsters get killed right away. It saves a lot of heartache and I don't believe you ever get a satisfactory answer as to why they did it.