Note: if you kill Drayek too fast, you will break the encounter and be stuck on this step until the instance becomes resettable (a bit over 2 days)!
Here is how I was able to kill him slow enough as a level 108 shadowknight:
* Mentored down to level 50.
* Removed all of my level-appropriate gear and replaced with lower level with NO STR.
* Used a level 10 weapon.
* Suspended my mercenary.
* Used only low direct damage abilities (didn't need to use lower level ones, just not the highest-hitting ones).