Somehow I missed all this interaction after I posted in December, but I do appreciate the discussion! I have been replaying it for the first time since patches 3 and 4 went into place and I've definitely noticed the changes. You don't really get the vibe that your companions hate you any more, there is much less of a teenage melodrama vibe, and the rivalry between Lae'Zel and Shadowheart is much more balanced. I've even managed to take both along and get high approval with both. I've also noticed that there is a direction to their rivalry. Lae'Zel mostly disapproves in direct confrontations if you side with Shadowheart over her. If you favor her she approves and if you remain neutral there isn't approval change. On the other hand, Shadowheart approving of something doesn't mean Lae'Zel disapproves, most of the time she could care less whether Shadowheart agrees with your actions. On the other hand, Shadowheart is more likely to disapprove of you when you say or do things Lae'Zel likes, such as approving of Githyanki libraries. This makes sense since it seems Shadowheart is in possession of a stolen Gith artifact, and is wary of Lae-Zel discovering her, and thus wants to limit their interaction. There are more opportunities to gain approval with Shadowheart than Lae'Zel though, so its fine to upset her a few times since you can more than make up for it.
As to being good aligned, having played DoS2 I know that Larian tends to make less static characters that are capable of following either a good or evil path based on the player's choices. The most popular character in DOS2, Sebille, seems similar to Shadowheart in some ways, and was not super liked in early access as she starts out as a cold-hearted and cynical assassin. You later find out way, and she has good reasons! She ends up being able to become a great goody-two-shoes heroine and is one of the more memorable CRPG characters ever. Shadowheart seems likely to have been kidnapped from a Selunite family and brainwashed, and will likely either continue on Shar's way or become a true hero in response to your character. As this is early access I can tolerate that its hard to totally judge a character's arc yet. On the other hand, the nitpicky ex-girlfriend factor was a legitimate concern, and it seems that this has been improved in my experience.
Also, I should say, I think its perfectly fine if I don't like a character, because there is probably someone else who does, and that's a good sign. I do think I judged Astarion a bit harshly at first. In all honesty, its your first encounter with him that is so badly written that tainted my view. Having played with him more I can see why some like him, and its fine if he's not ultimately my cup of tea, because that means a different kind of person is enjoying the game.