The comment I replied to discussed supersonic transport in general, not the obsolete Concorde. That's why my comparison used a hypothetical SST with longer range and higher cruising speed.
Range aside, wasn't the problem with London-Sydney that most of the route is over land, and can't be supersonic for noise reasons? At least, IIRC, that's what killed the Concorde in the potentially very lucrative US east-west coast market.
Heathrow-Sydney required a lot of subsonic sectors though (eg over India).
In theory Concorde could perform a one-stop Sydney to LA service (stopping at Cassidy International, Kiribati), supersonic the whole way.
Concorde had a range of 3900nmi (7200km/4500mi), a 777-200LR has a range of 8500nmi, an A340-500 HGW has a range of 9000nmi