I've written a simple explanation, as simple as I could make it, on why the new Mastery system is actually not a nerf in the amount of actual healing we do on average. I thought this thread would be a good place to link it:
I'll repeat the main conclusions from it:
1. The DA shields that the new DA system creates are actually slightly larger than the old system, even more so the more mastery you have.
2. The average healing you do will in fact go UP if you were focussing a lot on mastery, and will only go down a bit (about 6%) if you had completely neglected mastery and had fully focussed on Critical Strike.
3. The average amount of PW:S will go up if you have focused on crit, and will stay about the same if you have focused on mastery.
For those unfamiliar with the changes:
1. PW:S can now crit, for double the amount of shielding
2. Our mastery is divided in two parts: One part increases our healing, by a percentage equal to 0.32 times the old percentage (e.g. 40% -> 12.8%) and another part increases our shields by twice that percentage (i.e. 0.64 times the old percentage, or 25.6% in the example above). I like to describe the net effect as "smaller shields, on bigger heals".
3. A critical heal no longer heals for double. Instead, the base heal remains the same, but now we receive a DA shield equal to that heal times our shield mastery factor (1.256 in the above example). So instead of having the shield be 50% of the doubled heal, it's 100% of the normal heal.
Explanation of how the Crit Effect meta works now, and how Atonement is affected, here:
Consequences for stat weights (math heavy) here: