Heathrow is not a hub in the traditional sense. An airline like BA has the lowest transfer percentage of all the major airlines in Europe. This is great from a yield point of view (used to be, before this whole mess went screwy). As a reference Amsterdam serves more UK destination than Heathrow does. And out of the total traffic flow there are more UK residents onboard any KLM flight then there are Dutch people. For transfer (especially terminal transfer) Heathrow is a major nightmare.