Agreed- it wasn't the companion lines that were the main issue, though it's nice that they were fixed. It's really Tav doing absolutely nothing to help.
Yeah, I guess you can be roleplaying a Tav that doesn't care and would choose to just let him run off. So a choice would be fine. But I would argue that you aren't given that choice with Karlach. The character runs over to her in distress automatically. Obviously this is what almost every player would choose, and I think this has to do with the fact that her entire story is leading up to that scene so the devs want you to see it which makes sense to me, but there's still a disconnect here with how the scenes are treated.
I remember someone saying that they always had Astarion in their party but Karlach had stayed at camp the whole time, so while they were invested in Astarion's character they never got invested in hers. And it was weird for them to be prevented from doing anything when Astarion runs away, only to be forced into chasing down Karlach. I'm fine with Karlach's scene not being optional but I imagine that would make the experience even more jarring for the player.