I'm a Canadian living in Australia.
Australia has much more than just Atlassian. Canva is the 9th most valuable private company according to crunchbase [1].
But you need to look deeper than just "who has the biggest most successful companies. Note, the comment says "countries that understand software".
From what I've seen, and one of the reasons I moved here, Australia values quality production. They understand where software drives business and invest in that.
I'm former NICTA/CSIRO, and those organizations used to be drivers of technology and research.
Canada is a major technology hub. Microsoft and Facebook both have major development centres in Canada. Of course, being so close to the US, most of the brain drain goes directly out of the country, but that is part of the country and the people understanding the value of software. The education is good, and so people go to where the dollars are.
Canada and Australia are not going to be able to compete with the US from a dollar perspective. So many of the best Canadians, Australians, Chinese and Indian are going to end up in the US.
[1]https://www.crunchbase.com/lists/crunchbase-private-unicorn-...