I am no expert.
But when the UN was setup it was ideal with the aim to prevent another world war.
So it soldiered on but over time as other countries with hidden agendas lobbied and gained membership we saw a struggle for control of the UN to move away from the 'West' causing nations like the US and Russia, even the UK to exercise their veto vote, effectively blocking any UN action. Australia has not a veto vote that I am aware of. China does have a veto vote
Consequently the emphasis has shifted to NATO because, not the best phrase, they are western, Caucasian nations, not in a racial sense, but their ideals, moral standards, beliefs etc etc.
Why in the world Australia would want to chair the UN security council is beyond me but what do I know.
All you have to do is look at the past and current conflicts and where the UN is considering toppling legitimate governments because member countries have an agenda against that nation.
Iraq is a point in question, Sadam was a friend of UN until he fell out of favour, a couple of UN wars later to liberate the country and the country is back at square one. The Arab nations/tribes have been continually fighting amongst themselves since Adam and Eve and the UN wont stop that, its not what its charter was all about.
But I would be interested to hear points of view.
Seriously China could take the World today, look what Japan did in a few months and took what (atom bomb) and how long to rectify.
So perhaps we would need heaps of British and other warships once again.