Just want to let you know that the boss I mentioned above has been nerfed in today’s patch. Good call by Anet.
Patch changelog (spoilers!)
Story Chapter—The Departing: Drastically decreased the amount of health the Eater of Souls can steal. Story Chapter—The Departing: Increased the duration the defiance bar is vulnerable on the Eater of Souls's leap attack. Story Chapter—The Departing: Removed the Eater of Souls's ability to steal health from pets and minions. Bounties: Fixed an issue in which the Legendary Ellutherius Wintergust was unable to attack players.