"Teacher leaders need to turn around every now and then and look, if no one if following, they are not leading. And knowing a lot about topic is not helpful if it can't be explained in a way that encourages the right people to listen."
There is a critical difference between being an "expert" and "leader." Experts know a lot about their area of expertise.
But teacher leaders in formal roles are responsible for the direction of a group of people, and apply themselves in a way that allows them to constructively meet the challenges of that responsibility.