Blizzard has responded to feedback regarding the Restoration Shaman tier set bonus and will be reworking it for a future 9.2 build!
Blizzard Hi all, We’re planning to take the Restoration bonus back into the workshop and change it up for a future build. We want it to encourage you to Chain Heal sometimes and be rewarded for doing so, but the current 2-piece bonus is a little more passive than we think it could be. Read more on wowhead.com