while i have no issue with blackwater but i concur it probably annoy out of many.
Did you experience this "great" dungeon when the game came out? Since then, I think it got 3-4 nerfs. Previously, to kill the enemy, you had to use electricity damage. To be fun, the demons in blackwater were 100% immune to electricity. This meant that you had to use the coup de grace while they were lying on the ground. Given that the enemies have a huge save and sick amounts of AC (it has been reduced at least once but still has they have at least 64 AC) you had to roll 20. Nobody will tell me it was a good dungeon. Not only is it unlocked at the very beginning of Act 3, it also locks you in behind an absurdly high test for this level. This dungeon might as well have been unlocked in act 5, and wouldn't be much easier than the rest.
i played the game during beta till the first playthrough with angel. i intend to replay it again with trickster. had 2-3 playthroughs IIRC during beta. angel then lich if not mistaken. blackwater has alot of lightning wand IIRC. also the key for me there is greater invisibility which will deny their DEX bonus. i love pathfinder where many obstacles and solutions lies within the use of its spells. also my min difficult for pathfinder is Core which i find the bare minimum. Hard is quite annoying during early game. Unfair is a no no for me.
Originally it was impossible to kill demons with electricity. They were immune to electrical damage because of some strange reason. Honestly ac is not a problem in this game, the brute force method is pretty effective and don't worry about touch ac. Thanks to the broken mythic skill, you can easily achieve over 40 attacks in act 2 without favored enemy and similar bonuses. Sosiel is the most broken companion in the game along with Arueshalae. With the right amount of buffs you can even hit playfull darkness.
What the angel were you playing with or without the merged book?