Regardless of megafaunata, just by being in Australia, humans became an invasive species and did all sorts of damage that invasive species do.

Worse, indigenous Australians brought the dingo with them. Two very intelligent predators where two didn’t exist before did a lot of damage. Colonizing Europeans also did a lot of damage and nothing that the indigenous people in Australia did justifies what Europeans (basically just the British, let’s be fair) did, but pretending that indigenous humans aren’t as flawed as all other humans does them a disservice. It does not help indigenous people to put them up on pedestals and treat them as noble savages.