12 A350s is enough to fly the following routes
SYD-LHR
SYD-JFK
SYD-CDG
MEL-LHR
BNE-LHR
PER-LHR
With those routes, assuming they do happen (although I think double daily SYD-LHR is probably more likely than BNE) I don’t think EK, QR, SQ or others will be particularly concerned.