You meet Nettie who really doesn't offer any solutions except drink a poison and die. You meet a goblin in a cage who tells you she'll introduce you to her leaders, and you learn that they may have all the answers to your problems. Halsin MIGHT help you, but the cult actually KNOWS what's happening. If you help the cult, YOU might get to know too.
The big issue I have with the "Evil Path" is that, no, the cult clearly doesn't know what is happening. All of the True Souls have no idea they have a tadpole in their head, and even attempt to kill you if they notice your tadpole. (I'm assuming it's still like this...?)
Yes, the higher ups probably know what is happening. But it's very likely that the higher ups will look at you, see you're aware of your tadpole, and then just immediately kill you because you're a failed experiment and a danger to their goals.
People aren't supposed to know that they have mindflayer tadpoles in their heads. This turns the evil path into "Dumb Murder-Happy Evil" for me, rather than a broader "Evil=Selfish, but can still be smart about it" path, especially when there remain multiple options for otherwise healing yourself (Creche, Halsin, going to Baldur's Gate, etc).