As for transfer pax and their usefulness, from an airline point of view, they allow it to offer routes from its hub that may not be viable solely on origin-destination traffic.
I don't doubt that. My question was about whether or not it was worth building a superhub just to server more transfer passengers, as opposed to making do with what we have, and ending up with more point to point routes moving in to LGW & others. As long as it remains open, LHR is always going to have a certain %age of transfer pax, and a lower number will also pass through LGW.
Afaik, even at STN, where the locos officially want nothing to do with people making connections, 16% of traffic is air-air transfer.
Transfer pax are good business and there are many carriers that would not exist without them. EK, EY, QR, SQ, etc., come to mind, but there are many others.
All those airlines are focused on long haul. LHR-SYD would need a tech stop anyway, so much less difference between 'direct' and 'connecting'.
So whilst BA may well feed, say PHX from various points in Europe, they would much rather have o&d. Why? a) They are only paying one set of airport charges, and b) they will get much higher yields on the direct traffic as they are the only airline doing the route (from UK).