I don't see that either Qantas or Jetstar did anything wrong; there is an inherent risk with booking separate tickets and the risk is that of the passenger and not of the airline.

Jetstar was delayed/cancelled and rebooked appropriately according to their policies

The Qantas flight was an unrelated booking and so they operated correctly in referring the no-show passenger back to the agent that sold the ticket (AA)

It is lucky that the travel insurance treated the 2 separate bookings a connection and were able to arrange transportation on another carrier

Dave