Are you talking about compensation or duty of care?
Since all QF departures ex EU are long haul, compensation – if applicable – would be €600/pax. Now just notionally multiply that by the number of people booked on the affected flights and you will see why QF will argue exceptional circumstances with every breath in their corporate body.
For duty of care, though, 261 has no escape clause. You were entitled to meals and overnight accommodation until such time as you eventually got away, or cancelled your booking. This is supposed to be offered to you at check-in but there now seems to be a habit of leaving passengers to their own resources and letting them present their bills afterwards. Did you have bills to present?