Leadership is simply the successful way of working with people. That is one thing I have learned from getting past the half-way point of my doctorate in organizational leadership.
It doesn't matter if your leadership style is servant, transactional, transformational, or any other. If you work with a successful group, your example matters more than those in unsucessful organizations.
I don't mean that in a failing organization that you can't be a good leader.
I mean that the way self-improvement culture teaches is that successful businesses have good leaders and failing ones don't.
This is a mistaken thought.
Leadership is the more successful way of working with people. You can have an executive that is failing and still be a successful example-leader in the organization.
Leadership, simply, is what a leader does. It doesn't matter if authority is there or not.