Nobody is denying the importance of O&D traffic. Even at Heathrow, two-thirds of all passengers fall into that category.
But of the other third, very few are connecting between city pairs that would be remotely feasible for Ryanair, Easyjet, Norwegian, etc to serve direct.
So by all means dispute the synergy of hubs if you wish, but you will find few people in the industry who agree with you.