hi, I'm reverting this as it goes against past discussions within the local community, I would suggest to post in the OSM Community Forum if you'd like to propose a change or discuss this further.

For more context, in Australia we have administrative boundaries for "State/Territory" (admin_level=4) and "Local Governments" (admin_level=6), those are probably the only two levels used for "administrative" purposes. In ACT only we have Districts (admin_level=7) which can also be included.

When you consider boundaries set by the government you can add in "Suburb/Locality" boundaries (admin_level=9).

The "Sydney" place=city at https://www.openstreetmap.org/relation/5750005 and "Melbourne" place=city at https://www.openstreetmap.org/relation/4246124 cover the Sydney and Melbourne urban areas roughly considered part of those cities, although there's no formal definition so the extents are debatable. The boundaries aren't set by the government nor are they used for administrative purposes, so in actuality they probably shouldn't have an admin_level set at all, however we do and have been using 7. If you want to discuss this please do so on the OSM community forum. Further setting them as 6 would conflict with LGA boundaries which are also on level 6.

See also https://wiki.openstreetmap.org/wiki/Australian_Tagging_Guidelines/Land_and_boundaries#Administrative_Boundaries