I'm really surprised that everyone in this thread thinks Disc is a good spec. I haven't had much personal experience playing it myself, but a bad disc priest can easily ruin an M+ pug or a kara run, and everyone seems to think that this is where they do best in 5 man content. I don't trust the random pugger as disc priest anymore, and IMO it really doesn't have a place in PvE.
As for holy it desperately needs something. It really shouldn't be bottom on the heal charts and have zero utility. Feathers need to be baseline, and they need to introduce useful defensive tier in the talent tree.