I think you have made your points relatively well OP, but I just can't agree with you.
The narrative is different each time I play, if in one Astarion is shown consideration and respect and given support and becomes a less antisocial person then why is that not a legitimate narrative?
If he is not shown that and remains selfish, stuffed by trauma, and overwhelmed by revenge then why is that not also ok?
What should matter is how the world and other characters respond to the decisions I make - if I make different decisions and the same thing happens that is less meaningful of a narrative than what is possible.
Yes, it's a problem if every character and event only takes its cues from the player character, but I think you are wrong to suggest this is what the game is trying to do or is currently doing.
If all characters are asexual if the player doesn't romance them then that's weird and poorly done. But where is the evidence that is the case? ShadowHeart currently flirts with some companions and not with others, Gale thinks Wyll is full of shit, and LZ and SH have the beginnings of a significant feud.
There's no sign that the game solipsisticily revolves around the player - in fact I would argue that the whole origin character focus is leaning too hard to the opposite, that characters and narratives are too hard coded for there to be a strong sense of emergent role play.
