[PhantomGremlin]

It's true that the number or runways is "just one of the factors", but it's by far the most important one. The author's list doesn't really matter if Heathrow's runways are fully utilized.

So when the author says

   From Heathrow you can fly to seven places
   in the UK. From Manchester you can fly to
   thirteen. It's hardly a hub airport if you
   can't use it as a hub is it?

his argument is pointless. You CAN'T grow from seven places to thirteen places without being able to take off or land the planes!!!

The author keeps making the same mistake when he says

   You can fly from Amsterdam Schiphol airport
   to a whopping twenty-four airports in the UK!

Well, duh! Schiphol has seven runways, Heathrow has two. That's the biggest problem with Heathrow. It's full.