I have asked myself the same thing, KlarissA. When I played through the Act 2 romance scene, my first impulse was to click "Maybe you need a friend and not a lover" hoping this would open up a platonic relationship path. I was disappointed, when it didn't, and instead just ended the romance. The dialogue makes it seem like friendship would be the route offering more emotional depth, but instead it only creates more distance. This is doubly weird because the epilogue for the spawn-romance does give me the impression of a largely platonic relationship - but maybe that's just me.
If you are biased, then we both are. I did get the Act 1 scene at the party, so there was no line about him not having to repay me with sex, but there still was a discernible - and I think intentional - shift in Astarion's behaviour between the party and the moonlight scene. I would have liked to talk to him about it, to make sure he was alright but there is no option for it. Like you wrote "you have to be tone deaf and/or lusty, stupid even" going forward. Even if you are attentive, you cannot derail his little scheme before it can properly get started, the script does not allow it.
I recently tried the ascension branch, to get a first hand impression of what everyone's problems with the dialogue are about, and found it weirdly impossible to keep up a cohesive position or line of argument between the ritual itself and the scene in which Astarion turns the PC. The dialogue selection you mentioned is especially weird, because all of the points you can choose from, come completely out of the blue. I think, wanting to become a vampire and the outrage about being called pet (becoming a vampire has strongly been discouraged up to this point, and it's not the endearment that's the issue, it's the tone he says it in) are the weirdest to me, but as you mentioned, wanting his body is also odd. The Graveyard scene has a similarly weird moment, when Astarion suggests sex and you have three options to say "yes please", one to say no, but not a single way to suss out if he's really up for it again. You are also not told how the night went.
With the video of the panel in mind, there seems to be a lot of emphasis on envisioning the player in Astarion's romance as pretty horny. I have never played Durge beyond act 1, but I got the impression that the Durge/Astarion romance leans in more heavily into the horniness - but I might be wrong. Especially given the themes of Astarion's romance, of him just playing the rake, instead of actually being one, this seems a little odd to me, but maybe that's just me.
The game has definitely has also made me think about how I treat my companions. It most of all has made me think about how to portray a relationship that favours equality and partnership, in a medium in which the player by default has all the control, or how to write a flexible script with dramatic tension, when you cannot really anticipate the player navigating it.
