Any track in Sydney should clear 60 000 passengers per hour on 120 s headways. Nobody in the world runs 90 s headways.
Of course Melbourne coped: people are leaving on multiple tracks from Melbourne SC: base four, but six possible if using Mon.-Fri. instead of Sat. routing.
Full house at Etihad is routine, not a once-per-year event.
I haven't wasted time looking up the timetable for this group: the acid brigade can do that.
I spent the time watching a wonderful documentary on Dame Vera Lynn turning 100: far more heartwarming, and far more increasing my knowledge.
https://www.youtube.com/watch?v=hFSk42tmTWY https://www.youtube.com/watch?v=hFSk42tmTWY (with no fullstop).