No amount of gear or Versatility is going to save your raid from Mythic Kil'jaeden in Tomb of Sargeras. At least some amount of your raid needs to be able to live the first intermission.
The main issue is that you cannot burst down the boss. At 80% health, Kil'jaeden enters an intermission and takes 99% reduced damage. The main thing that matters here is the Rupturing Singularity purple balls. These purple balls can only spawn on the four corners and will slowly fall towards the platform. When they lands, it will knock all players away from it, almost the entire length of the platform. You'll need to be close to the ball in order to not be knocked off.
The intermission has 3 patterns of purple balls: a set of 2, a set of 4 and then a set of 2 and within each set, each corner can only be summoned once. The patterns are otherwise random and change from pull to pull. The goal is to get knocked from one purple ball to the next one, until a break in the action. You don't have much time to move after landing so make sure you get knocked towards the next one.
Everything else can be overgeared, just make sure not to get knocked off the platform.
