I think it makes sense why this change happened, not only for pacing reasons but also to purposefully reinforce Astarion's transactional way of thinking and behaviour. It fits that now he will always confess after Tav has done him a favour. He's lived that way for centuries and thus is still unable to act differently, it's instinctive to him. He's only beginning to learn that there are people who can be good to him without wanting anything in exchange and vice versa - up until that point he's only played nice to get something out of it. Not only it's a behaviour dictated by his tragic lifestyle, but in this case he also gets solid proof that Tav actually cares about him on a personal level and not just because of his pretty looks, therefore he feels the impulse to approach them and drum up the courage to talk about genuine romantic feelings (which is something he may have never even done before).
Although the post-Araj confession could use some rework, it still worked perfectly for my drow Tav. It happened at the beginning of the act, when they were still getting familiar with each other and ended up actually amazed and excited that something that started off for both of them as 'l want someone I can trust on my side and let's enjoy ourselves while we still can because we might die any day now' turned into something deeper. For some reason Astarion has nothing to say about Tav being a drow (which he totally should, because these elves have a terrible reputation and are known for having slaves and treating men like crap. I picked the 'he's all mine' to appear like a proper female drow as part of the cover to infiltrate Moonrise Towers. When Astarion reacted so strongly to Araj, for me it was the only roleplay moment where my Seldarine Tav could truly show him he was more than a toy and a tool.
To me post-Araj confession seems meant for morally ambiguous characters who end up following the drider (the confession is totally spontaneous and blunt with him being grateful that Tav is actually a nice and trustworthy person after all - at least to him) and post-Yurgir for good-aligned who go to the inn first (the whole monologue feels like it was planned and likely even rehearsed by Astarion for some time - he already knows they are a nice person and believes they would prefer him to be soft with them).
