People fly into London airports with onward travel to many place not just London.
Who said anything about London? Luton is in a better place for the majority of the country than STN, and so will always have that advantage, no matter how many bells and whistles STN gets.
I was referring to the comment that LTN may become the "Le Bourget of London" (i.e. lose it's airline services) if STN got a second runway. If it is left to the market (i.e. no articifial intervention), it will never happen because of LTN's location