Maybe on retail. In here, disc priests are beyond absurd.
Power Word: Shield stacks with itself. I'm full griev on mine and I put up 200k shield, so 200x2=400k on average.
Divine Aegis, if procced once, gives a normal 80k-ish shield(with my gear), but if you overlap it, the shield is 4x better, so around 400k.
That's 800k absorb in 3 instant casts, no mana consumed, no effort, no risk of getting interrupted.
Holy is bugged too, since you get surge procs if you stay in your Chakra, but compared to Disc, Holy is actually killable by a solo good DPS, disc is impossible to kill on your own even if you play UH DK :)