And what about the distribution? Is it 35% +- 5% across the board, or 90% for some routes, 5% for others?
I have no idea, airlines are hardly about to release that kind of data. But even if we accept, for the sake of argument, that the percentage varies widely from route to route, that hardly constitutes proof of the blanket proposition that transfer passengers don't add value.
Few would argue that UK Plc doesn't need a hub airport at all, and a hub (by definition) is an airport with a significant proportion of connecting traffic.