So reducing the
dmg modifier he gets with 51 traits: -25.5%
dmg increase passive -5%
dmg increase [Forbidden Flame] -10%
dmg increase [Will of the Conclave]
it is quite accurate to calculate his healing.
Goal: 53322 > 21813
Math:
-53322 x 0.745 = 39725 x 0.95 = 37738.6 x 0.9 = 33964.78 base dmg
-33964.78 x 0.56.1 = 19054.2 base heal
-19054.2 x 1.05 = 20006.9 x 1.1 = 22007.6 final result
(small derivation as 56.1% mastery could actually be something between 56.05%-56.14%)
So can confirm that artifact
dmg modifier should not increase atonement healing.
Here people discuss about this topic too and say that passive weapon
dmg did never increase atonement heal:
https://us.battle.net/forums/en/wow/topic/20758447049
Regarding 7.2.5 changes to give disc also 15% more healing like all other healers the
dmg increase from these traits does no longer count towards atonement too.
Maybe check a few more videos to 100% confirm this, no time to dig deeper rn.