I think teaching is a skill by itself. Effective teachers usually grasp the theory behind the learning process, while this is not necessarily true for expert practitioners. There is much more to this: knowing how to communicate effectively, how to keep learners engaged, adapting to your students etc. This means a person can effectively teach the basics without having deep technical expertise, it's simply not the most important skill in teaching beginners imo.

So assuming those are somewhat independent skills, you can find skilled practitioners and skilled teachers but in my experience it's hard to find someone with that skills intersection. I consider this kind of people quite exceptional.