I generally try to avoid playing as companions (it just doesn't make sense as it is not exactly team-created RPG like Solasta or Wasteland2&3/IcewindDales), so I didn't run into it.
I think what you are running into now is Astarion as a companion and Astarion as a playable character - of course Origins haven't been fully implemented yet, so it is difficult to say how much of Astarions unique content will there be. nor if it will be accessible if he is played as companion. I honestly have no clue what best solution would there be. One character being playable main protagonist, a companion and playable companion is difficult for me to wrap my head around, as all of those three things call for different things in my mind.
