DS is ESSENTIAL to the proper healing rotation. Without a single doubt, if I didn't use DS in my rotation then I wouldn't be able to hit 1 million healing + consistently. It's wasteful to sit their and wait for your energy to regen, it's nearly impossible for you not to bottom yourself out while throwing CC's, slows, and keeping 4 stacks of 2 SRM, while throwing big heals.... you can't keep your energy up without using DS. And Cool Head should be an emergency, like after blowing 3 kolto packs back to back or throwing a Kolto Cloud after several big heals. Never as a "Oh, I dropped a little low, let me force myself to -20 energy to use it."
That is what separates the 500k healers from the 900k+ Healers.