I think SH and Astarion unfortunately are the only characters for which the writers could somewhat explain them being "fine" (pretending to be fine) with poly when they needed one female and one male character for Halsin. Which automatically makes them candidates for being "fine" with the drow orgy and Mizora.
I find that reasoning by Larian to be faulty. Iirc didn't they say the NPC companions weren't romancable with each other? So again rules or whatever are being bent/broken for Halsin. Every and all problems stem from Halsin, the root of all issues.
