Yes, if you have a heal that is a dps gain you generally use it on cooldown to gain the max amount of damage. If you want to design a defensive type of ability my advice would be to 1st make sure it doest have the same niche as other cooldown (this one for example overlaps with Essential Dignity as 2 single target burst heals), 2nd you dont give them any kind of dps gain, they have to be dps neutral at best so its used to heal/protect instead of a source of dps and 3rd you make the defensive part consistent, you want to be able to plan around that reduced damage and in order to do that you cannot have a chance that it doesnt reduce damage.