Probably because Hunters tend to shoot us Warlocks in the head while we tend to nuke their butts :) Seriously though I noticed that too during beta, but it is a nice rivalry as far as lore goes. During beta every piece of green armor I had made some reference implicitly or directly to Hunters, making fun of them, criticizing their methods in someway, stating how are Warlock method is better etc. However, it does makes sense if you consider the following: From what we know us Warlocks are essentially the Sages of the Traveler and harness its power purely for intellectual reasons, hence we're philosophers at heart and love the knowledge bequeathed to us by the Traveler. Weaponizing it is secondary to us. Thus we're the brains behind Guardian resistance to the Darkness. Titans arguably are the brawn of Guardian existence, but protectors of the Traveler--which is exceedingly important. So if us Warlocks are the brains / scholars and Titans are the brawn / defenders, then what are Hunters? Well Hunters are essentially loaners, drifters, and out for themselves with no real or at least definitive purpose as to how they help the Traveler. Hunters are also fundamentally explorers traversing what's left of our civilization's remnants, and utilize the Traveler's light to punish our enemies. In essence Hunters are really traveling around trying to make our universe safer for us again, all by themselves--definitely a most important task. Thus in a sense I think Warlocks and Hunters are diametrically opposed to each other philosophically; Hunters see harnessing the Traveler's light for knowledge sake as a superficial use of this power whereas Warlocks see harnessing the Traveler's light just to simply destroy our enemies as an excessive waste of what it should be used for. This is totally speculative on my part and just my 2cents, but hopefully we'll find out more about this rivalry post 9/9.