I feel that the PC should have additional dialogue options or insight. To me it does not make sense for the PC to say "oh sure" or to say "do it yourself" and immediately turn your back on someone you have only just met. The PC does not know at the time that Astarion is a vampire. When experiencing other conversations, the PC can do a variety of things such as insight, reading body language, wisdom, intelligence, survival, etc, that for some reason do not come into play with Astarion, but can be used everywhere else.
The way the Astarion encounter is setup to me makes the PC seem inexperienced in the world/life, and then all of a sudden after the encounter they can use their stats to make numerous checks in dialogue elsewhere. Even as far as checking other party members for deception.
Take Shadowheart for example, if you are a certain race she absolutely hates you, but you have options in dialogue to potentially make her friend or foe.
I am sure there will be more things added as this is early access, but my only complaint companion wise (if I had one) is the lack of conversation options upon initially encountering Astarion. Something like "sure ill help," "no do it yourself," "deception check," "Insight check" etc would make it better.