Simply from how many things drop, I find it most effectively to dodge into the mobs, mirror image, shatter, followed by frenzy. And then slash away in the middle of those mobs. If you're downed, you'll instantly rally, and keep on doing it.
There IS a risk of dying, and then people being not nice/in a hurry/lost in the crowd and not rezzing you, but... Hey, at least you can get more loots that hopefully cancel out the repair bill, and more.
Or you can just use a greatsword and hope for your iBerserker target to live longer than a second (and if you target the veteran/champion, well, it won't die that fast, but your chance of aoe damage to the other mobs just dropped significantly). Sometimes it works.
PS: I've got an elementalist and it's really not THAT easy to tag things. Problem is, things die too fast, that 1 second cast time that plagues most of the elementalist's skills is really visible. Plus, it's not like elementalists can switch weapon, and bleed/burns just don't tick enough before the mobs die (sometimes they do, which would be great, but a lot of other times direct damage is way more efficient). This means that if you just want to run events as an elementalist, you use a staff and stick to fire/air/arcane. And that makes you utterly miserable when you find yourself not in the presence of the zerging group and alone with a bunch of staring undead.
Guardians and warriors, by far, are more efficient, and there's just not much that can be done without overhauling their mechanism. My guardian gets drops from almost every single mob spamming 3 on Greatsword. I'm sure warriors do it even better.