Agreed that Act 3 isn't great with approvals in general... and generally lacks the same hyper-focus paid to each character that had me fall head over heels in love with this game in Act 1. (My standards are forever changed. Nothing will ever compare to its magnificence.) If I'm sad about anything regarding Larian's trajectory forward, it's that we're probably not getting a Definitive Edition that cleans up Act 3 and adds in all those missing camp scenes and companion interactivity.
Minthara and Astarion are the biggest offenders, but there's times I'm fussed on Gale, too (who's a less severe case of divergent character growth that doesn't align with his reactions.)
That said... is Stephen Rooney the only person who could conceivably write Astarion well? No. But he is a much fiddlier and self-contradictory character than, say, Lae'zel or Karlach. The only other origin with his level of constant mental gymnastics is Shadowheart, and she's already coalesced into a clear good/bad path by Act 3. And I'm not... especially trusting of his character handling? There's been a trend towards making him more... unambiguously good and satisfied with everything in his good ending from release to the current state of the game, when I was happy with things being less perfect and still having a lot of messiness to work through. He's a case where I would want the original hands on deck, because splitting his Act 3 mess into a character-development-in-progress path and a 'still the same terrible person' path invites a lot of opportunity to simplify the character, and overall? With how Astarion and Karlach's stories have shifted from launch, and how Gale and especially Wyll changed from EA, I think Larian is maybe a little too susceptible towards nice-washing the characters to please fandom. So... perhaps I should be careful what I wish for.
Though I'll still lament that you can force Astarion into sex and then have him approve of saying you're a nice person.
...I always thought Astarion approved of Tara eating pigeons because Let The Predator Eat, lol.
