As the title suggests, I am starting to question why I am stacking mastery. 90% (made up number) of all raiding Discipline Priests are stacking Mastery. To me this makes complete sense in 25 man raids where you aren't able to cap out Spirit Shell on the entire raid, but why is it so important in 10 man raids where you can easily hit the absorb cap?
Raid buffed I have about 60% Mastery (I'm in the armory under the same name). It takes me three PoH casts on each of the two groups to hit the absorb cap for Spirit Shell. If I reforge/gem out of Mastery it puts me around 40%-45% Mastery raid buffed. It still takes me three PoH casts on each of the two groups to hit the absorb cap for Spirit Shell.
The only time it seems like the mastery would be beneficial to Spirit Shell in 10 mans is if you're using it after the damage has already started so as to get the biggest absorbs per PoH cast as possible. I do my absolute best to always have Spirit Shell capped before the big "OMFG the raid exploded" boss ability goes off. If it's not capped it usually means I messed up... In which case I'll probably forgo using Spirit Shell and instead use AA/IF, PoM, and PoH spam (possibly with barrier) that way the CD on Spirit Shell still lines up with the next big boss ability.
I understand Mastery also affects PW:S, but that doesn't seem all that amazing as I'm mainly just tossing it on the tank(s) for the extra mitigation and Rapture procs.
I also understand that Mastery affects DA, but without the crit to back it up that seems negligible to me. :/
It's starting to feel like both Crit and even Haste would be a better choice for me... I'm only 6/16 Heroic so far (all regulars cleared of course), so I don't claim to have seen it all... But is there something I'm missing here?