A Lock going to be less efficient from 1-40 than say a Paladin or a Mage, however as soon as you can go into ZF with your gang of nublets the lock will outshine all other classes.

A warrior is pretty good in ZF with dedicated healers, a lock however is better, faster and easier.

All you need to do is drop 2 or 3 dots per target and the target dies. A lock can benefit from a healer in that they can push the pace harder. However a healer is not required if you have good gear. You will do around 100k an hour with a Lock in ZF which is better than you will likely do in SM with a paladin or a mage. You can do ZF into your 50's to boot.