I do not see Astarion as necessarily a bad person, as his actions are mostly driven out of fear of Cazador rather than his ambitions. His search for power, not liking wasting time on helping peasantry and such are all the result of his fears because he under no circumstances wants to return to him as a slave again. It's why he is so jumpy all the time and has outbursts.

He did afterall spend the last 200 years being tortured and starved on a daily basis. That kind of mental and physical torture would mentally break people, so if anything I admire Astarion for keeping his sanity and remaining semi-decent. No denying he is changed slightly for the worse and self-centered, but realistically that kind of torture would create a murder hobo who would never trust anyone again. Like a badly mishandled dog that bares its teeth at anyone who tries to approach it with love and care because it no longer trusts humans. Yet with time they grow to trust once again.

So I see him just as I saw Sebille. An innocent elf taken against their own will through clever machinations and enslaved to be used as a tool to do inhumane things. Who naturally end up broken, jumpy and untrustful because of it, but they slowly start to open up more and get to show their true selves to the world eventually once the emotional wounds are healed. Sebille went from cold and distanced deadly assassin to an affectionate good-willed puppy by the end of the story.

Or just like Visas Marr in Star Wars KOTOR 2. A pure force user and only survivor of her race, taken and corrupted by Darth Nihilus who Meetra Surik later saves. Visas becomes once again a pure force user with proper hope and ideals and after the story she brings back her dead wasteland of a planet back to life with the force.

I also do not see Lae'zel as bad either. Considering her teachings and culture, she is actually doing splendidly all things considering. Like her remarks about her cutting our tongue out for interrupting her or skewering Zorru. People might think of these as shallow jokes or threats or think it is her personality speaking, but they in fact show her morals by breaking protocol and Githyanki customs. By Githyanki standards she is quite merciful, respectful and nice and gives us leniency when it comes to not understanding her. She even grows to like us and admire us as time goes by, especially if we take interest into her culture. Not to mention she already in Act 1 starts seeing Faerun slightly different than when she first arrives.

So yeah I honestly do not think any companion so far is evil or bad. Neutral at best, but they are so misunderstood and judged way too quickly. Minthara might be the only evil one, but I doubt she might be fully because she is afterall controlled by the Absolute and doesn't know it. I assume we might save her from the Absolute later and show her the way.

What I am trying to say is; people can change and it's too early to judge them. In Larian games some start as douchebags and slowly become fantastic likeable people that are like family by the end of the game. I absolutely loved Sebille and Red Prince stories for example. Very well written and quite memorable moments with them.