lolz
Sure, you can kill a mob way faster than me. But while you're casting spells and shooting your wand while running away from that one mob (or wasting even more mana on PW Shield) until it dies... and then drinking (and this is after you had to run away because you pulled two at once), I'm on my third of the group of six I just pulled, and haven't used 25% of my mana yet.
And don't worry about needing to drink half way through a trashmob fight in BRD, I've got enough healing power for the entire group and can do it while offtanking. So yeah, you might as well go Shadowform ¬_¬
Now, Druids on the other hand... they can heal. But Priests? Shackle an undead, Shield the tank, and get in line and Wandspam, biatch.