Disco Stu,
Pretty sure anyone who understands ATC has said it here many times before, but just in case:
Rule 1: "It's about the Runways"
Fiddling with enroute Airspace in Australia means & does nothing to delays.
Rule 2: " ATC don't delay aircraft - other aircraft delay aircraft"
A Departure slot time is not about delaying you - it is about saving you money, because some other shiny jet wants to land just before you - and one right after you. When you are on the freeway driving your flash Volvo whi do you blame for the delays? Usually whoever built the infrastructure or lack of it. It's the same deal.
Rule 3: " WX conditions X Available Runways (X Political Runway Configuration) (X ATC Staffing!) = Runway Acceptance Rate.
Runway Demand less Runway Acceptance Rate = delay (plus unplanned or unplannable events: pilot initiated missed approaches due non-wx related issues / MED1 EMERG / Aircraft returning to land EMERG / Insert Here)
A 2 minute slot that is not avail is not a 2 minute delay for one aircraft - it is a cumulative 2 min delay until excess capacity exists again.
It's simple really.
Solution = more runways (stop closing airports Government! Councils!)
Solution to Delays Does NOT = Lobbying, Cutting ATC Numbers, New Whizbang Enroute Software tools, Flex Tracks, ADS-Bblah blah blah.
Ask anyone in the USA - they will tell you the same.