Here's what bothers me: this fight was already difficult but beatable, and not necessarily by cheesing, but it's definitely not going to be your first playthrough, because if you play like the story would lead you to, you all walk in together like lambs to (literal) slaughter. Only way I have won (not trying crazy shit like sending in two invisible imps, etc.) is to put my spellcasters up top, and make liberal use of potions of speed and strength. But now, when I see BS like an alleged 5th level NPC with 91 HP, I have to throw the BS flag. There is no way any 5th level character can amass 91 hp; therefore, any NPC with 91 hp is not 5th level. If Larian is going to insist on putting adversaries that are that strong (and hostile) on the battlefield, they need to assign them the appropriate level, and reward EPs accordingly. If I roll up a Gith fighter, best I can hope for at 5th level is either +2 Con bonus and the Tough feat (+4 HP per level for a total of +20 hp for a 5th level character) or +3 Con if I take a Con score bump for my ASI. They could give a 5th level fighter max HP for every level (which ain't kosher), AND the tough feat, and still be 21 HP short. BS.
I will say, since the latest update which puts all the gith in gith half-plate, I am now inspired to create a run-through where all four characters can wear half-plate by the time they hit the Underdark. (Tav, Lae'zel, Shadowheart, and either Wyll or Astarion with Moderately Armored Feat from 4th level ASI. Not going to Stealth anywhere, but don't need to!
