If I remember correctly from one of the videos or features on the classes, the hunters used to be considered "Outlaws" before they became guardians while the Warlocks are basically the scholarly types. As you said, it is probably some rivalry based on how each group used the travelers light (power). As for the Titans...well we're too metal to worry about these things. Get it? Cause Titans wear mostly armor? Metal armor? I'm off to go die now.