So I just had this sudden theory about the Parshendi. My theory is that the Parshendi are there to train the humans. Think about it: They always fight with about the same amount of people, even though they can use larger armies if they need to. They killed Galivar, took credit, but Kaladin calls them very honorable. So I believe that kike the humans trained the Parshmen to serve, they trained the Parshendi to train them before Odium comes again.