But whilst you are talking growth and looking into the future, LHR is at capacity NOW and was when the original application was approved years ago.
Enabling more capacity at LHR will likely free up capacity at Gatwick so you solve more than one problem. This is why LHR makes sense.
It is not, and never has been about sticking a runway somewhere in the SE. It is about creating a hub that can give access to the regions and is the reason 40 regional airports are behind the plan. You say that is a supremely terrible idea and the SE should be given extra runways that only serve the SE yet you then say;
Interested parties argue that English regions already deprived of state infrastructure investment for two generations will be locked out for at least another decade if projects in London are allowed to monopolise national funding yet again
So the argument against the imbalance of funding spent on London & the South East is to deny a nationally beneficial project and instead just give the SE more flights?
Just because you and others choose not to believe that the regional flights will be forthcoming does not make that so and we can all make up arguments to support our choice. The truth however is that LHR want to create the infrastructure to support these routes and the regions want to have them. That is a win/win for the whole of the UK as far as I and many others are concerned.