walnut
your points are well made, & I have no issue with them.
What I meant to convey was that the REAL requirement is for ONE large London airport (perhaps replacing both 'KK & 'LL). This would have been the Thames Estuary airport, or something similar. Apparently, that has been ruled out & the choice for expansion lies between 'LL & 'KK.
In these circumstances, the only "solution" would be Heathrow; since choosing Gatwick for expansion would not result in the actual required solution, which is ONE much larger ( than 'LL's present size) London airport to compete with the continental airports for "hub & spoke" & connecting traffic.