Yes, I think that the aviation noise issue (locally) is overblown though it is true that most European capitals do not fly airliners over the centre. The pollution is another matter but should also include traffic for balance but never does.

Re expansion for Gatwick: is that a LHR Gatwick Terminal idea? If so then a security nightmare. You would need to segregate transfer and normal passengers in different parts of the train but even that is probably a non-starter (once upon a time you could check-in baggage at Paddington if taking the Heathrow Express, very convenient but clearly a security risk). If it isn't integrated with the terminals then you lose the aviation hub - you might as well just close Heathrow in that case and we will all pay much more for foreign flights and London loses a competitive advantage.

Don't have a history of agreeing with Boris but I think he happens to have it right in this case.