There's this idea that Warlocks are underpowered compared to the other classes. While I can't say for certain, I can compare them to the most similar class, the Ranger while using a bow. Both have an ability that locks on a person and does extra damage to that person. Both have the Prime Shot ability. While the Ranger has a +2 proficiency bonus from the bow, the Warlock can attack against Will, Fortitude, and Reflex.
The difference is mainly the sort of effect you do with attacks. Rangers largely move themselves around, then do plain ol' damage to the target, where Warlocks do all sorts of effects to the target, but don't get any bonus to maneuvering or escaping.
As far as I can tell, Warlocks actually get a bonus that the Ranger lacks: where the ranger can get a bonus from a magic weapon, the Warlock can get a bonus from an Orb and a Wand, cumulative, so far as I can tell. In the late game, that really adds up.