Increasing numbers of people I know on this side of the world (New Zealand) who make an annual pilgrimage to visit our UK grandchildren, chose to enter and exit Europe through errr Europe. In our case, France. If that trend develops we should see some reduction on the pressure at Heathrow.
Aussies know all about Ford versus Holden and always these posts degenerate into Boeing versus Airbus. For what it is worth I have flown Qantas A380s Sydney to Heathrow a number of times and they have always been full. So what does that tell you?