Sorry Lead and other folks, with all due respect, I believe there's a mistake in your calculation:
Ah statistics.
According to the FAA, there were 25,212,000 [OK, let's assume that figure] general aviation hours flown in the USA in 2018.
Let’s round the numbers and say that Australia has 1/22nd [[b]Incorrect: US population is 327m, Aus population is 25m, ratio is 1/13] of the population of the USA.
24,212,00 divided by 22 = 1,680,000.
With the correct ratio, one has 25,212,000 / 13 = 1.94m hours
According to BTRE, in 2017 (the most recently-available stats) “general aviation hours flown by VH-registered aircraft [in Australia] decreased by 3.6 per cent to 1.20 million hours”. 25% less than in the USA.
And adding another 314,000 RA hours to the VH ones, that's 1,200,000 + 314,000 ≅ 1,500,000 hours flown, or a 23% decrease per capita over the US [somehow Squawk7700 got the right figure].
With 90% of the population in Australia being urbanised vs. 80% in the US, I'd further normalise the ratio to 23% * 80/90 ≅ 20%, because the dispersion of the population in Australia is such that fewer people live in rural areas.
Of course a truer picture of the reality would have to account for what one really understands by "GA is booming". Flight training to foreigners for instance is one field that largely benefits GA in terms of hours flown but will certainly not help GA uniformly across the country.