Hunters and Warlocks both rely on strategy and knowledge in their battles (That is the characters mentioned in grimiore) The rivalry has gone on for some time before the example of the Ahamkara, but thats where I read about it first. Basically the Warlocks like to boast about what they find and show off, acting like they are the best of the best, but the moment a hunter sets out to do something similiar they succeed (Ahamkara case) Whats truely enjoyable about this rivalry is that people read it in the grimiore and put it into practice, Bungie effectivly made a rivalry.