it appears to me that it is a case of people doing their very best with an unnecessarily constrained system
That is Australian aviation in a nutshell.
The Australian Government takes a bureaucratic approach to aviation not a pragmatic one.
Your whole question about being cleared to land is a classic one. In the US they give the responsibility to the PIC to not land on top of another aircraft. Over here a controller has to make that decision for the PIC which is just one more layer of bureaucracy but it costs time and runway space.