You're asking the wrong people Dick. RAAF airspace, their requirements, their procedures, so ask them.
Being able to plan something does not guarantee you'll get it or without delay. Assuming he'd planned overhead WLM, MDX would still have been delayed because the SY sector would have knocked him back for exactly the same reason. The delay was not caused by no plan. Why would the pilot have waited any longer before tracking the way he did as that would have been plan "B" in case of clearance refusal? The outcome would have been no different.
And seriously, the only constant in our job is change.