What caused it is simple. The warlocks and hunters are like brothers and sisters. Some times they want to stab and slap the crap out of each other, but when an unlucky cabal gets between them... The Titan pulls the cabal's boots out of the ceiling. The titans are kinda like the older sibling that moved out and just kinda watches on with bemusement as the other two spat over who is better. All in all, all classes have their skills and i like them all. It just takes a proper touch to use each class to their fullest advantages. People who see a "master class" just lack skill in using the other classes to their true limits. Even I've yet to master the Titan like i have the hunter and warlock, but i can't wait to do so!