i think it doesn't matter how hard or how easy a paper is, the most important thing is, can the person who took the paper, performs?
it could be a case that CPA australia thinks that their paper, with that standard, it's sufficient for them to perform in accounting jobs.

Ultimately, the most important thing is how much you can absorb, analyze and apply your knowledge through these courses into work.
You can have all the professional certificates, but you're nothing if it's not being utilized in your work.

just 2 cents

U can have ICAEW, ACCA or ICAA but what deferentiates you from the others is still YOU. not the paper.