I'd say it's medium on potential sleepy quality. I can definitely feel their limitations in PvE once I hit the +8 range. There is no room for error on mechanics in melee range and I did a King's Rest that didn't feel doable.
They are going to be a real fun comp though for PvP.
For PvE I'll most likely revert back to Elemental as being able to be ranged has such a large upside to it.
I'm also still on the fence with DK's, being all tanks for Mythic + was quite fun, the damage was just a bit low. This disparity was very noticeable with corruption as true DPS started to really pull away from tanks. I'm now wondering if a 4x Frost DK / Prot or Holy Paladin for PvP would work and then use Blood for Mythic content.
The good news out of all of this is theres lots of options and I'm excited for that.