I am not aware of all the details of your awful experience.
It is a very interesting story as sad as it is to hear.
The management on property should have been removed long ago. Hyatt allowed in one of the friendliest and service oriented cities in the world this business culture to exist for years
The bigger problem lies IMO that Hyatt itself has let customer service ethics erode at some of their hotel levels and within Omaha to the lowest levels historically.

Hyatts attention isn't with Consumer/Guest Relations, customer service or hotel experience other then decor & f &b options
It is with getting the run down poorly noise insulated AmeriSuites refabbed into Hyatt Places and the Andaz brand up and running.
Focus on customer service for three to 4 years has taken a back seat as those at the corporate level feel those elements can be neglected and guests will still come and support the program and the brands.
This is not to say that there aren't some excellent Hyatt Hotels who do a superb job......there are without a doubt.

Some wonderful upbeat bright professionals still shine within select Hyatt properties that make the brands proud
But the way I see it the Park Hyatt brand is no longer of interest to Hyatt
No new Hotels in North America and what they had in LA and SF is long gone
Sad Sad Sad

Back on topic I agree with your assessment that if there is anything positive left about the Park Hyatt Melbourne it is the upgrade system for Gold Passport Members.That is the one thing they do very well.