If you want healer engagement then you need to make it so tanks don't have as much self sustains as they have right now. The way content is designed make it so most of your ''healing'' gameplay is just keeping the tank alive. The lack of sustained damage just made it so you don't really have to heal any dps unless they don't have enough hp to survive their next screw up.
Like it hard to feel meaningful in most content on the game when Nascent flash exist on a 25 sec cd with no ressources cost to it.