I still can't really find anything on pervasive violence amongst Australian aboriginals although I've done a fair amount of searching. I did however, find this about Papua New Guinea:

"Agriculture was independently developed in the New Guinea highlands around 7000 BC, making it one of the few areas in the world where people independently domesticated plants.[25] A major migration of Austronesian-speaking peoples to coastal regions of New Guinea took place around 500 BC. This has been correlated with the introduction of pottery, pigs, and certain fishing techniques."

https://en.wikipedia.org/wiki/Papua_New_Guinea

So, that is in line with what I said in my OP. Sedentism/agriculture leads to hierarchy as well as a change in other social conditions that make the preconditions for violence a lot more present.