Disc on mythic plus is amazing, almost every group I've been with says they love my disc. You have to talk to your tank to go 1 pack at a time, I usually say "Mr. Tank I'm a disc priest, I'm most effective when I can heal through atonement, please pull one pack at a time. I usually end on 150-200k overall dps after the dungeon, this is for m6-9. On 10+ there's more shadowmend spam.