Ideal types, not boxes. Shaman and priest are poles drawn to make comparison possible. Almost every real specialist sits somewhere between them — and can be thoroughly priestly on one axis while remaining thoroughly shamanic on another.
A word about the word. Shaman is Evenki. Outsiders borrowed it and stretched it to cover practitioners across the world who have their own names for what they do — mudang, shapori, hataałii, oungan. It is an analytic category, not a translation, and many practitioners do not use it of themselves.