I'm going to agree with something starryophonic wrote, which is that relationships can be complex without introducing problematic content.
I'll also out myself somewhat by stating that I am a submissive and a masochist. Most of the time, when I see kink portrayed in media (be that literature, video games, or what have you) it's poorly done and misrepresents how much of a role consent, trust and negotiation between partners plays in the relationship.
I think it's fair to say that Astarion (UA and AA) touches on themes of dominance and submission, but without fully engaging with them (the game flirts with the subject, but doesn't explore it beyond a few winks). I think it would have been interesting to embrace the subject more, with Tav and Astarion having at least a conversation about preferences and boundaries.
One of my gripes with UA has always been that he turns fairly vanilla, as if the kink was just part of his act. Which bothers me on several levels. At the most basic, there's a subtle implication that kink is somehow 'wrong' in that only an evil character would partake. It would have been nice to see UA and Tav engaging in some dialogue about what he enjoys/wants to explore now that he's decided a physical relationship with Tav is back on the table.
I think that gets to a lot of what bothers me about the AA hate discourse. I definitely feel this twinge of kinkshaming to the criticism. I mentioned before that a clip of post-Ascension Astarion telling Tav "you await my command" seemed to instill a lot of ill feelings in people who don't prefer that path and is one of the many pieces of evidence presented that AA is abusive (and to be fair, some folks who like AA don't like that line either). I'll out myself a bit too and say that line felt like it was speaking directly to my kinks. Every time I re-watch that scene you pretty much have to peel me off the floor.
And honestly, and this is something I'm fully willing to admit could be me reading way too much into it, but I read a little bit of kinkshaming into some of the companions' reactions too. Pretty much none of them approve of the Ascension, which doesn't mean they don't approve of D/S, but there's this air of, "Astarion is clearly evil now. I can't quantify in what way he's more evil than before (again, the 7k souls could still die even without ascension), but just look at him!" Very Willow from Buffy, "I'm a bloodsucking fiend! Look at my outfit!"
I think you hit upon something interesting here. It seems safe to say that Ascencion is *intended* to be Astarion's evil outcome, the way that being loyal to Vlaakith is Lae'zel's and becoming a dark justiciar is Shadowheart's. It could be a thing where the writer's felt that this path (which involves participating in a literally hellish ritual) was self-evidently evil enough that they forgot to show the fullness of why. Personally I think his full going over into evil is also obvious based on who he was and wanted to be before, given how he basically says at multiple points that he thinks having power gives you the right to abuse it, but that's just me. It can easily be argued that the game broadcasts Astarion's evilness post-ascencion without actually getting opportunities to show it. It's tougher to do that when he's still under the control of the player as part of his party, but he also demonstrated that left to himself he'd be evil anyway so it can depend on the viewer. I think that Wyll suffers the same fate but to a worse degree because there wasn't even any pre-establishment based on his character beforehand. There's a weird vibe around his politician outcome at points as if that's meant to be his evil ending, with the game seeming to assume Wyll's motives are entirely different to what he's shown at any point. Probably in part a consequence of the rewrites.
