It's the "no matter what" there that does it, and what part of fully committed to his own freedom doesn't make him chaotic, if he was fully committed to other people's freedom that would be classic Chaotic Good, no?
I think that the difference between being neutral, chaotic, and lawful can be pretty murky but the difference between Chaotic Evil and Neutral Evil, to me, is usually some kind of principal you'd put over yourself.
I'm always down for a good redemption arc, I don't understand the people who've said that its a tired trope.
I think the "no matter what" part is exactly what makes him a bit lawful. He does NOT compromise on it. There are no such commitments on the chaotic side of things. It's spontaneous. However since Astarion is both somewhat spontanenous and somewhat commited, I would settle on him being neutral on the law-chaos axis, and evil on the good-evil axis because his goals are all self-serving, even at the cost of other people's lives.
I think commitment and chaos don't really mix, because there is an expected consistency. Consistency leads to regularity, regularity tends towards lawfulness.
