Falling Icicle
Adventurer
Very well summarized. And it is a shame. Warlocks are fairly simple to stat out, they'd make wonderful replacements for BBEG casters to save prep time, but they really are awful in that role. They do too little damage per round to be threatening at the assumed CR, and have too many HD and special abilities to honestly get knocked down by more than a few points of CR, either.
Don't forget that warlocks can take 10 on Use Magic Device checks. A warlock can be far more threatening as a BBEG if he is armed with some scrolls and wands that contain nasty spells.