It just depends on how you're using cooldowns really. HE doesn't overheal very often, and there's a lot of fights where there's things you *could* DH... but you can also just guard those things. If there's not more than one thing hitting hard every 30 seconds you don't really need more than guard, and in that case HE is more useful since it won't ever be a full overheal, and when you couple it with our 4pc it can cause you to have a very potent heal between the purify proc and HE.
I know in 10m that it's often more benificial to run HE as it causes my healers to have to pay even less attention to me. Between Beacon transfers, Chi Wave, EH, HE and our 4pc, BrM doesn't need much attention in 10m at all. There's some fights where I've found DH to be better (malkorok and juggernaut are the main ones) but it doesn't really feel all that strong when you can just guard most big hits anyway.