The team I am refering to is 5x Blood DK, yes. That is not to say you could not run something else and do just as well if not better (for example Xeneres did very well with 4x Blood DK and 1 Prot Pally, Chibilukina did very well with a Druid tank, 3 hunters and a resto Druid). We only have a small sample size of people pushing high level mythic+ dungeons so no definite answers are available.