Dps spells (and buffs/debuffs...) are as core for the healer design as heals. They are what we do the most, those spells are the most demanded actions of the whole kit by design even at the highest level of content, the dps contribution is what gives most of the healer systems a meaning in the game (cards, lillies, aetherflow...) and they are the focal point of every tiny bit of healer optimization. They are as core as it can get and it makes perfect sense, you can't heal an enemy to death.