Hans the world is not a fair place. The RAAF has been hiring pilots for a long time. They know what you need to pass the course, and what you need to have a successful career.
Someone totally focused of being a RAAF Pilot with no interest in being a NAV etc, is not a lesser candidate to someone who wants so badly to be in the military they would take any job.
You either pass the selection or you don't. If you don't, it's a personal choice what you choose to do next.
But I agree with you about someone thinking doing badly in the non pilot tests is somehow going to help their application. They would seem to have some gaps in critical reasoning, and perhaps a different career choice would better suit.