I'm not familiar with what happened in Melbourne.
But, setting a 55t floor for entry or advancement completely disregards mission compatibility. 55t and above is a broad category. wouldn't it be sensible to be more specific, for example:
55t -104t = 2000 hours
105t - 159t = 1000
160t or greater = 500
Wouldn't a sliding scale as such provide more flexibility for advancing current crews and hiring future crews?
This is just as arbitrary but at least more specific.