Well said. If you look into some of the research and theories on leadership, you find a very different picture. You could someone a leader any time they have influence over people toward a goal. With this in mind, you can see that an "individual contributor" can definitely be a leader.
However, in business, leadership is often conflated with "legitimate power" (as opposed to expert or referent power), meaning that the person holds a title and is assigned direct reports. Titles and employees are not necessary for leadership.
I wish that engineering departments were better at highlighting this. A person with practice and experience can be a leader by simply working hard, setting a good example, giving input in team meetings, etc.