"The one aspect of the Australian method that baffles me us allowing aircraft to depart outside of their slot."
One of the many things that baffles me is an Australian controller is how overseas long-haulers depart on their slot time, we have 'trackmasters' in the hallowed "National Operations Centre" aka NOC who approve wondrous flextracks to allow aircraft save time and fuel, the then the same boffins at the NOC run ALOFT v3 aka "SEMAP" to tell which aircraft are non-compliant with their Sydney arrival times!
How brilliant do you think controllers feel telling them they are 10-30 minutes ahead of their time, only to have some slow down and be overtaken by trafic that should have been sequenced behind them. When Sydney Flow does arrive at 5am, they promptly ask WTF has happened?
How embarassing..