From my experience, maximize AVD and physical DEF, equip him with a dagger that boosts MND with an effect to use to increase magic accuracy (Spellstrike), and let him spam shutdown magic (stop (ice magic), shackle (fire magic) or petrify (earth magic)). With cheap HP and MP restoration skills, he can finish the job extremely well. If MND is not high enough to guarantee accuracy after Spellstrike, then sacrifice some durability for more MND. In this build, Warlock cannot deal much damage himself (he can deal some mild damage by using Draconic magic) but I think it is much more rewarding to shut down enemies with nearly 100% successful rate, since, according to Lanchester's laws, it would be much easier to win the battle after shutting down some enemies. Actually I think Warlock is too strong...
As for the boss with full ward, you may use the water magic that inflicts leaden + slow + RT delay, and it would be easy to kill the boss then. Besides the debuff magic mentioned above, there are a lot of useful supporting spells as well...
To say some digression, to shut down Cleric and Knight (who may use Divine magic to cancel shutdown state), you may use male Spellblade or Rogue with weapons having Sleep effect (a fan which is a variant of Dagger, and a blowgun) and employ their guaranteed attack skill for themselves and hit to make Cleric and Knight sleep. Or you may use Archer or Ninja to silence them with the help of Art of War.
