Exactly, you wouldn't put up with it at home, not even on a holiday to an unrefurbished hotel in the Balkans. A forum such as this allows others to report similar experiences and perhaps levels of black mould will be included on future cleaning checklists across all QPs. This is a much better outcome for the airline than a covert camera story on a current affairs show. Reporting it to some manager isn't going to get the CBR QP showers looked at. It's a system-wide quality control issue.
Perhaps others can look at showers in lounges and bring it to attention here. And maybe others at the Dom SYD J lounge can give their opinion, it is after all subjective opinion in the end. My level of mould tolerance may be different to others, in the same way a dead pixel policy is.
Ultimately it's probably as simple as repairing/cleaning/installing good ventilation. You prevent these things through ventilation, don't you, not replaster the ceiling every 12m.