The main issue with healing power is that it scales horribly:
The highest on the wiki I found for non-self only healing scaling is a pathetic 0.75 scale outside of druid whose heals are so big they don’t really need healing power and their best healing power scale that I have found is only 1.22.
With hp being in the 10-20k hp range and a full set of acended healing equipment with druid can barley push your healing done by 800-1000(Note: generally with all other classes it would only push it by barely 400-500 more healing per 20-60 second cooldown which isn’t noticeable at all)making it REALLY FREAKING BAD and generally not worth using
Until they increase the scaling to make it worth while because extra 400-500 healing or even the better 800-1000 every 20-60 seconds is pretty horrible.