Maybe gearing for mastery in raids is not so crazy for Restoration Druids for challenging progression content.
In progression, players are often at low health. With the Cultivation talent, a Rejuvenation on a party member at low health is already 2 out of 3 of the HOTs for Restoration Druid mastery. Add in a Wild Growth, Spring Blossoms, Cenarion Ward, or Lifebloom, and you are getting full mastery benefit.
A few Restoration druids I have talked to are using a Mastery heavy build on at least some fights. I don’t have all the answers here, but it is something at least worth thinking about.