Make healing hard, then let's talk about the importance of Cleric Stance. Healing is the only role with down time in party play. DD's are ideally always maximizing DPS along with tanks to ensure timely elimination of threats, while tanks also continue to build enmity over other party members. Healers can only heal damage as it comes in, and have only a few choices of what to do during down time.

1) Do nothing, sit at full MP
2) Do nothing, wait for MP ticks
3)Use DD spells, inflict trivial damage
4)Use Cleric Stance, inflict meaningful damage

Take away Cleric Stance, and healers are left with largely a waiting game, playing whack-a-mole with HP bars, then going dormant until the next burst of damage. If healing posed more of a challenge that actually required you to keep your wits about you, this would be less of an issue, since healers would be occupied anyways. Bosses have been trending towards being more challenging (WP HM second boss has a short rotation with pretty damaging moves that can get out of control pretty fast, especially when mechanics are mishandled), but between overly simple trash, bosses, and massive overgearing, healers just aren't taxed hard in average content.

Cleric Stance remains as a great skill that chips in substantial damage while dealing with the copious amount of downtime that healers experience. It allows me to execute a meaningful action every GCD, something that both the tank and DD roles are expected to do. The only way to change this is to give healers actions that are more meaningful than killing the enemy, like some form of active buffing, or make things hit hard enough so that healers are forced to, well, heal.