They take more skill in pve. Really they just play differently. Warlocks can just come back to life, spam flameshield. Same with Titans and their shield perks. Hunters have invisibility which is extremely useful in Prison of Elders. Gunslinger is basically a glass cannon, and one of the best orb producers if your warlock is saving his self rez. Bladedancer has near infinite invisibility, which makes it the medic class. Note: these classes are not good for camping in a corner, they are best used on the move, using high agility to stay out of harms way and clearing mobs. Titans are support, and warlocks should be either dps to the boss, or orb producers. Self rez anywhere but hard raids is a waste.