Prophead - Passengers from the West Midlands, NW England, North Wales and Western Scotland arrive at Euston. It's escalators, tube trains and luggage issues for them. And those pax who do arrive via the ECML into Kings Cross still have to change trains and stations. But since you're clearly happy with enroute chages of this sort, presumably that means it is similarly fine for Londoners to change planes at Dubai, Bejing or Doha when they need to reach a secondary destination. All they need to do is cross a terminal floor! Who really needs a thin long-haul route from Heathrow?
Meanwhile, you appear to reject forecasts which indicate future loss of direct flights from regional airports as implausible. Yet you're fine quoting numbers such as "£187Bn in benefits" attributable to R3 projected over sixty years. Do you not see the irony? Is it just long-term forecasts which don't suit your preferred conclusion that you object to?