Marielle:
Oh, I do understand Astarion, that's why I personally don't think, ascending him is the best route for him. You can see that differently of course, but I'm amazed about his character growth, when you encourage him and set an example at being better ( for a good playthrough). I did choose for him and my redemption Durge to go on adventures after the game and had a really amazing epilogue.
I'm not asttached to him or other companions like some people here seem to be, but I like all Origin companions and Jaheira and Minsc. The only companion, I actively don't like, is Halsin, since he doesn't have any content outside of romance in act 3.
And Astarion starts out at being insufferable in act 1 , if you play good. You can even call him out on it. And no, I don't need the companions to be wholly on my side, I actually liked in BG and BG2, that companions leave you, if you play against their alignments too much. Here, you only have that with the good aligned companions and if you actively ignore companion quests.
I mean Astarion attacks you at first meeting, do that does set a tone and I'm honestly very ok with it. He has no reason to trust anyone to be in his team.
Shadowheart is much more unfriendly to you, if you don't free her on the Nautiloid, which is understandable too and Lae'zel is acting mostly efficient. Plus she and Karlach are the most open about their motivations and backstories - and you can loose Lae'zel very easily at several points in your playthrough
She even can attack you in the crčche, if you choose the wrong answer.
As far as I know, Astarion does that too, if you simply interrupt his ascension without giving him arguments to think about. So there is at least some reactivity about how the pc handles the companions quests,
So basically,all companions can and will leave you or attack you, if you decide against their fundamental beliefs without reason ( Wyll and Karlach will just leave you, if you side with the goblins). You can get every companion to leave, if their approval is too low or if you go against something important to them, so that is similar to the first two games. They don't ambush you, that is true, in some cases (Astarion, Lae'zel and maybe Shadow) they will attack you directly in certain scenarios, so I agree, that an ambush situation would be nice. For example Wyll and Karlach teaming up after you side with the goblins, to get the artifact from you, that keeps the party sane.
But I don't see the companions as slaves, blindly doing,what you want. There could be even more reactivity, agreed, but there is already a lot in the game and companions can completely change, depending on the route, they go,which is also good. I mean look at us: you like AA, I like spawn Astarion and we both get a character,we like. I call that a plus.


"We are all stories in the end. Just make it a good one."

Doctor Who