But we are being told that Heathrow is the saviour of the UK and if we don't expand it then we will all be using Ansterdam/Frankfurt etc.
We already do and Manchester too. That's passenger choice and should not be dictated by the government or the owners of Heathrow.
Heathrow isn't trying to be the saviour of anything. It is merely doing what businesses do and trying to capture the extra income from thos who as you say are transferring via Amsterdam and elsewhere The benefit to the UK is the extra income generated as well as extra routes that then become viable.
If there are enough passengers coming down from Newcastle for a flight to Salt Lake City then an Airline will fly direct. That is supply and demand. Nobody is dictating anything.