(...) and potentially Astarion/Minthara romance players very unhappy (...)
That's what I have been pondering about for a bit. I can't say much about Durge, because I lost interest in that very quickly, but for the neutral/good Origins who end up with Ascended Astarion and then make a grab for the ultimate power, it is very hard to not read Astarion as at least part of the driving force behind this shift.
I can only say it with certainty for Avatar-Gale, in who's case Astarion is written as the devil on your shoulder, who encourages you to consider your own will over Mystra's, who's word about controlling the artefact at the heart of the cult run through your head before going to sleep and who praises you oh so prettily for every power-grab you make. It's a shame that they simply had the romance drop for Avatar-God-Gale (especially if said god is also a vampire lord's spawn) but not having him (romanced Ascended Astarion that is) feature prominently in the Absolute ending, would be giving up the subplot that started in act 2 and could now be realised. (Maybe even with some back-stabby action by Astarion if you didn't control him but also didn't become his spawn akin to the House of Hope ending, or some allusion to him planning to puppet-master the newly minted Absolute.)
