Melbourne and Brisbane is as busy as any airspace in the USA
It is not, Dick. Hence, the remainder of your post is incorrect.
Some of the
city-pairs are quite busy eg. Melb/SY, SY/Bris, but that's it. The US has many more city-pairs in the same volume of airspace. A common misunderstanding, and an excellent demonstration of how statistics can be used to baffle the uninformed.