I haven't played the game seriously since WoTLK (and even then, I can't remember past DKs being SUPER overpowered at the start)
Looking at level 100 DPS charts right now DK seems to consistently be at the bottom. Since vanilla, I've found that history is typically pretty accurate (For example, warrior tanks always being OK. Mages / Locks / Rogues topping DPS, etc)
So can I expect DK DPS to be low-tier DPS for legion or is the current state of them kind of an outlier?