To be honest when you put it like that I absolutely cannot disagree, you raise some really good points there,
it's making me want to play the game again and re-analyse!
I do have a little theory that depending on the path you go on (whether its "evil" or "good") it might have an effect on your companions morality, (if they dont leave you for being a dooshbag or too evil, which to be fair is the most fun play through) but that might play into the companions arc.
But with Astarion have a few loose screws does make sense, that boy needs therapy. (They all do)