The 4-piece requires us to do a 2-step process for it to work. First: Prayer of Mending. Second: FLASH HEAL. No priest is going to get a Flash Heal off in rated battleground at high rating. And because of our horrible mana regen, we can't afford to NOT spec into Mindbender for the 1 minute Shadow Fiend. So we can't get From Darkness Comes Light for the chance of instant flash heals. So right now, the 4-piece is just absolute garbage.
Not even going to start on the abundance of INSTANT CCs in this game right now. I'm stunned/silenced/disoriented for 75% of the time.. which is why I get no flash heals off. I only get as far as Prayer of Mending my target.