I think raid groups is where disc will shine. Going in a 10 man group but cant decide between 2 healers or 3? Disc priest is a perfect choice. Going with a mythic group and 20 people, disc will be a solid utility by providing both a DPS boost as well as healing boost. 5-man's don't really let 1 single class shine more than another as much as a raid can, and I think disc will fit well in raid groups.