Astarion and Minthara is the perfect partners in crime for a evil playthrough. I never felt the need to call them out. Maybe I did in my first goodish playthrough, I can't remember.
I also didn't necessarily feel the need to talk to Astarion about his psychopathic score or discuss it with him haha. Joke aside, there are a few moments where you can call him out a bit, as others mentioned before, e.g. whether he envies Cazador (which indirectly implies whether he would also like to have that power or is as ruthless as him), and especially up until act 3 he usually reacts in accordance with his character (like Narcissism, Machiavellianism, and only sometimes with a bit empathy) or in this case, agrees. Or after ascension when he is told that one tyrant replaces another, when he honestly admits it. (Which I do really like! It shows he is very self-confident and don't feel the urge to lie or to hide. Or he doesn't even take it as a critical comment). If he could have been called out on other occasions, he would have responded in the same way, I would assume.
Apart from the spawn route, which I don't like for certain reasons, I think Astarion's reactions are mostly pretty brilliantly made and, thank God, he doesn't lose his narcissistic traits in the ascending route.
I can imagine Astarion being a bit annoying if you are strictly playing a good Tav, much as Karlach is a bit annoying on a evil one.
No, for me, not at all, but I have my own taste. The only thing, which sometimes was a bit annoying, when playing a good Tav, is, when he disapproves on your good choices. But he never said annoying things, on the contrary, he showed a great interest in my naive and shy Tav (even without much approval) and so he seduced him really early in the game, and before the party. I loved that. It was well done by Larian.
As for gaslighting, never felt that.
I think this word from the op is a strong one and probably has a negative connotation, I think what we see in the game is a stylistic device in making an evil character interesting and loveable. Like, the game or story doesn't focus or calls out so much on Astarion's evil behaviours, and it's surely not made in a negative, but in a positive way or thought: To create an evil character, which can be liked and romanced by players. Also in movies and other fiction, when the intention is to create a villain, people but should sympathize with them or should find them very interesting (sooner or later), they for example would probably not focus on the suffering of the victims. Because if the focus would be too much on the victims and you would feel empathy with them, you would not sympathize with the villain and start to disgust him, at least, the majority. But using this stylistic device doesn't mean, that people, who indeed like the villain, would not recognize this, most people know and understand, what's right and wrong.
