If you look at RPGs and MMOs, magic users are often the strongest characters, just think if Warlocks had an ability to transform into the enemy you have your cross hair on and the enemies think your one of them and stop shooting , and in PvP you appear has an ally to the enemy team for a short time, Warlocks have so much untapped potential to be nightmares for AI and PvP alike, that's why Bungie is so scared of buffing them But it's probably down to engine limitations