I think people are dealing to much in absolutes. It seems he's content is designed to be beatable without healers DPSing. Of course if you add dps, while maintaining the appropriate amount of healing, then that would be a more optimal strategy. Think of it like getting an A on a test, using healer DPS vs getting a C or B without, you still pass, its just that you could have done better. So if your healers can swing it DPS by all means, it creates a larger margin of error for your actual DPS classes to pass the dps checks, and increases odds of a clear, as long as needed healing is maintained.