In all honesty, if there were an instance where DoH/L were useful in a battle to make it go smoother, it would more likely only occur at one or two points in the instance, and not throughout. Or at least, that's how I would design it. So, the DoH/L used in one battle would most likely also have a DoW/M for other battles in the same instance. Ideally, the use of a DoH/L in a boss fight would be an optional method for victory, gaining only a slight advantage over a tank-n-spank zerg-fest. Enough where people don't feel the need to have them, but certainly utilize them if available.