Also, Both SCH and WHM have a healing boost CDs. (Fey Illumination and Divine seal)
If you compare them with Synastry, Synastry, which is a cool and useful skill, becomes horrible.
I'd sooner compared Synastry to Selene/Eos' Embrace rather than Divine Seal or Fey Illumination. Embrace is a 300 potency heal every 3 seconds on a secondary target, available all the time (unless you for some reason let Eos/Selene die). I'm not sure exactly how that can compare to Synastry and burst healing in a given time frame, but since it's 50% of only direct healing (other than yourself) it's probably more comparable to having faerie healing on a single target for 20 seconds.