I suppose if you were to put a gun to my head I would probably say there are 3 main characters with separate story arcs and a lot of supporting cast. But they all have their own story arcs too which is why I considered them mains
The word "protagonist" is generally defined in such a manner as to admit multiple characters. In a book with multiple story lines, each story line may have a protagonist (or more than one protagonist), for example. The word "main" seems to me to imply, by definition, a single person. I submit that some books, like Steven Erikson's Malazan books, have many protagonists, but arguably don't have a "main" character.
