Example: Astarion has been a member of my party for everything for every play through, but only just now have I received the conversation about beheading vs poison or stabbing.
Could be just me? But thought I'd mention it.
Missing Astarion talking about beheading is not due to SH's presence, but to the fact that if you don't long rest at least twice before you talk to Nettie, the scene will be overridden by something else. At least that's how it has been for me in most of my runs. I hope Larian will fix this because camp scenes shouldn't be so easy to miss.
Or you could have simply spoken to Astarion last... the last companion you talk to will often leave out part of what they would have said if you had spoken to them first. But I really can't remember if that's the case for this convo as well.
Aside from that, yes, SH usually overruns everyone else, which is maddening for me. I only recently had the second dream without SH and got to see a cutscene I'd never seen before...
I'm not fond of the current design style that demands that only one party member gets to respond to something, to the exclusion of everyone else.
I'm still not sure how I feel about that. On the one hand, I hate missing out on companion content, but on the other hand, it's nice to see new stuff in another playthrough and I know I'm going to play this again and again and again. What I really cannot stand is the fact that one companion always takes precedence on everyone else. If they really want to keep it like that and only allow me to listen to one companion reaction per event, they could at least let me choose whose comment I want to hear.