I don't think it is, that's part of what they're paid for (granted it's rare) - even unarmed members of the public tried to tackle the gunman, it likely would've saved lives - I'm not saying they needed to have run right up to them - the detective took his shots from 40 meters away AFAIK and using a tree.
We've seen the same thing in the US, a 6 minute attack and the officer responsible was prosecuted as a result - in his case they've obviously got some active shooter SOPs he was supposed to have followed, in the Aussie case maybe not, they perhaps were technically correct and following inadequate rules/SOPs (but these are armed officers so that really ought to be looked at else why are they armed...) - either way it's frustrating to see that some of them didn't take the initiative and act - thankfully the detective who arrived did so despite seemingly doing so alone and also only armed with a pistol.
Scot Peterson is thought to be the first US officer ever charged with failing to respond to a school shooting.
www.bbc.co.uk