Yes. I'm in the start of act 3 but haven't finished the game. From the responses it sounds like there isn't a BG1 / ToB mechanism in the game where embracing evil led to one set of powers and resisting it led to another.

@leidra2. On taint and disgust. Mind flayers are evil just like vampires, werewolves and ghouls. If you get bitten by a ghoul or werewolf you have so much time to cure yourself or you are lost to the evil. To refuse to do so - to avoid and cure and lean into the disease and transform into a werewolf to embrace evil. Thus embracing the tadpole taint cannot be a good act.

I know that you are fond of social psychological theories of morality and I suspect that you are diagnosing me as someone who confuses disgust with morality
(I think the confusing-disgust-with-ethical-decision-making theory and the set of experiments that "support it " are problematic at best btw)
but such theories don't apply in Faerun. Monsters are inherently evil and choosing to become a monster is an evil act. Or, you are wedded to that theory, then it's the case that basic psychological 'mistake' - conflating disgust with immoral acts - is built into DnD. The Larian artists really leaned into the disgust factor but mind flayers aren't just ick, they're evil. Always with exceptions if you want exceptions - apparently Omeleum changed alignment at some point . . .

( and yes, I'm annoyed we can't smite the necromancer in the circus - imagine if one of those funny dancing skeletons was someone you loved)

Most games implement some sort of measure of this - each evil act costs you a few points and if you reach zero you change alignment or die. I haven't looked at the new Ravenloft but I used to play with my old group in 2e Ravenloft - if you committed 3-5 evil acts the powers of Ravenloft would claim you and you would be granted a realm and a set of powers. (please roll a new character - your old one just become an end boss)

Bioware combined the ravenloft powers system and the Zharakia honor system to create the BG1-2 reputation system. But, if I am reading these posts correctly, not such system exists in BG3. Which is a significant departure from both BG2 and from EA.

You are right that it's also a stupid decision!