I have only played my Druid to 15 and, since you alrady got that perspective, I will not comment.
I have a 21 Dark Elf Defiler that I am enjoying at the moment. He does not have the regen or power-heal capabilities of the other 2 classes. My strategy has been damage mitigation by use of wards, which Defilers do get. In addition to the general ward, we get an instant cast, no power cost emergency ward, which is nice. I also chose the better ward as my level 20 training spell and it has made a difference IMO.
We do still heal, but I always heal in conjunction with the single and group (did I mention that?) wards. The wards can also generate a decent amount of aggro, so you will be working with the tank to manage that. Group heal is OK in a pinch. I usually use it in an emergency - like to give the tank more time to peel an over-zealous mage type - or at the end of a battle to get everyone's health back up if more than one party member had aggro during the fight.
Defilers also have some maintained buffs, and offensive debuffs and slows. SoW is always nice. At 21 I CAN main heal in Fallen Gate, but I can't daydream while I do it, especially in high aggro areas with the occasional over-pull.