Apologies up front before I offend anyone. I have mainly been raiding Holy in a casual guild with 'ok' progress (tier 11 cleared in 25) and tried to heal encounters on more than one occassion as Discpline.
My main hindrance is that the healing throughput is so reliant on cooldowns and that the absorbs (and thus mastery) is basically garbage at times, i.e. proccing Divine Aegis which doesn't gets used. In particular for stuff like healing up after a raid wide damage pulse - the DA is wasted since there's no damage following the pulse fast enough.
If anything, i'd like to see DA work more like EOL. Instead of letting it fade and let the absorb go to waste, let it turn it into a heal on fading (sort of like Lifebloom does). Or just increase the buff timer long enough. At least the mastery wouldn't be so useless then and i'd have more reliable throughput.