With Echo defeating the penultimate boss of the Sanctum of Domination in just 22 pulls, many players and fans are disappointed with the tuning of the raid, but that's not to discredit the high-level of tactics displayed by the European guild.
When players were testing the new raid on the PTR, they noticed a new trinket from Fatescribe Roh-Kalo which had a very interesting passive tied to it, and knew they would see it used in high-end raiding.
How Echo Achieved World First Kel'Thuzad
The Weave of Warped Fates trinket returns players to life if slain by no more than 40-60k (depending on item level).
Echo had this trinket on certain DPS players in the raid, and would purposely taunt the mobs that spawn from the Soul Fracture mechanic.
The way the fight should work is the targeted player (tank) is hit by Soul Fracture, which spawns clones that cast an uninterruptable raid-wide AOE until defeated or the inflicted player is slain.
Many people guessed this mechanic would be cheesed with battle resurrections and ancestral protection totems, but this trinket makes the strategy more reliable and less punishing.
Because Echo was able to defeat the encounter with this strategy so fast, Blizzard won't change how the trinket or ability works as it is seen as an unfair advantage to the guilds who were also close to a kill at the time.
This falls under the term "clever use of game mechanics" while not completely abusing a clear bug.
Similar encounters are being compared to this like Helya in Legion, where a player was sacrificed to completely remove one of her mechanics, which saw many top guilds banned at the time.
We may potentially see a fix for this during the weekly reset, or even a few weeks from now or Blizzard might choose to ignore it completely.