Just like the Beholder in the flask he isn't immune to frightened.....which means like any tough fight in the EA atm......Lae'zel just solo'd him smirk
Since both fights are optional and out of the way I would suggest to make him immune to frightened.
Rather have them nerf the minotaurs that swarm you at the featherfall entry point in the underdark after the spiderqueen fight.