I think that, in a video game sense (which is really the only context where the distinction of "player characters" makes real narrative sense,) "sidekick" type characters probably do tend to be NPCs. But I think this is a major weakness of using a video game framing for the concepts under discussion. Problems are rarely solved in real life the way they're solved in books, but they're pretty much never solved in real life the way they are in video games.