My take is that there are some things that need to be improved and that we need more balance between the two paths/options.
The way Astarion is presented and talks to us, he is an unreliable narrator of his past before Cazador. He can't even remember the color of his eyes and barely talks about a "boring past as magistrate". That could be a lie, a partial truth or him not remembering much. For all we know, he could have been a corrupt evil magistrate, a neutral/selfish one, or even a chaotic good that pissed off the wrong powerful people and was defamed to get rid of him. We do know that after the supposed gur attacked him, Cazador turned him. But vampires turn people to use them, for fun or even to enjoy corrupting and destroying someone good because they get pleasure out of that. The truth is that all he can remember is being a slave to Cazador. Act 1 is the first time he is "free" from Cazador and he is testing what he can do and that new "freedom". He is also trying things and learning what he likes and doesn't like. But in this act, he is still heavily influenced by Cazador and what or who he made of Astarion.
In Act 2, Astarion realizes for the first time that he is not yet free from Cazador. He still uses sexuality as he was taught, he still behaves as he used to be when he was a controlled spawn. And he thinks as he was taught. This is common for both Ascended and not ascended. We do know that Astarion thinks that power would free him and allow him to do what he pleases (that is what he believes). But does Astarion want power and control or just to be free? That is what his dilemma is about. Does he really want to take Cazador's place or does he want to be able to decide his own place and what he wants to do? I think at this point not even Astarion knows.
In Act 3 it is clear that Astarion needs to get rid of Cazador, both literally and figuratively speaking. The trick here is that we do know that the Ascension ritual was a pact with a Devil and thanks to Wyll we do know that those pacts have strings attached and you end up being in debt or forever trapped/linked to the Devil that offered the pact. Which is reinforced by Haleep and Raphael. There are always unintended consequences to those pacts. And that leads us to the 7000 spawns whose souls are meant to be sacrificed. In D&D sacrificing a soul is worse than "just" killing someone. You can raise someone from death, but if the soul has been consumed, that is no longer possible. A soul goes to their god/goddess realm to enjoy the afterlife, but not if the soul has been consumed. So consuming 7000 souls is not a "mercy killing" (although someone can rationalize it as that to not feel bad) and doing that might taint, change, or consume part of the soul of the people doing it. Plus, you don't know if there is another "Maryzora" who would "pop up" after to demand things from the person doing the ritual. Cazador doesn't go into detail about the pact in his diaries, so going along with the pact is like going along with using the tadpole powers. Larian chooses to not have consequences for using tadpole powers and might choose to not add additional consequences for the ascension ritual, but it perfectly could be like Wyll's pact and have "small print". We do know that Astarion is impulsive and usually jumps at the chance to get power, but that sometimes he doesn't really want it if there is a price to that power. That is why you have a chance to persuade him to not ascend (and you should be able to explain to him that he might be losing his freedom or part of him if he goes along with the ascension/pact.
Both choices are valid, ascend him if you think that it is what he wants or tell him to not ascend if you think that it is not what he needs and that what he needs is freedom to re-discover himself. At this point and after ascension/not ascension is the very first time that Astarion is free from Cazador, but even now he might still need to get rid of his influence. And here is where I think Larian confuses Astarion development with Tav/DU character. While Larian should write Astarion, his words, and action as they see fit (origin is tricky, because that should be decided by the player), they shouldn't decide how Tav/DU (player character) react to what Astarions says/does. And they fail both Spawn and Ascended Astarion. With ascended people have explained how disappointed they are with Tav's face in the new kisses. With Spawn people complained about joking/laughing when he burns. And we don't see Astarion personality/changes there.
My suggestion is if they wanted to show AA dominance, then maybe they should have tried to make HIM demand a kiss from Tav. Or him asking Tav/DU to wear some revealing/stylish clothes for Astarion at camp. Or even showing possessiveness in situations like Harleep, Maryzora, and Halsin. Example: Tell Maryzora that Tav/DU only has sex if HE says it before Tav has a chance to answer. And him putting down Maryzora. By the way, exerting control usually means being less free, because you have to devote your energy and attention into that. The second you relax that control, you might lose it. So you can't just simply disappear for one night to enjoy dancing. Or if AA disappears one night to create spawns to use in getting power in the city, when he comes back, he would probably interrogate Tav/DU.
On the other hand, Spawn Astarion might want to try new things with Tav and propose things to do. Like spending a lot of money on things he likes, asking for presents, or stealing things he likes to gift something to Tav. He can even ask to do/try things for his sake. So what if he was the one who wanted to have sex with Halsin? Or even try a threesome. That changes the dynamic. Or he might start doing pranks on other companions and Tav. Does Astarion like music? or art? Does he likes dancing? Someone who suddenly is free after so long being a slave might want to "try everything" and "do everything" just because.
So have Astarion do things that reflect his path once Cazador is no longer there and then let Tav/DU react as they see fit. Offer choices for Tav/DU and let the player choose. And try to balance time/resources invested in each path so fans won't feel neglected or that there is only one "real path"/a path worth playing.
To sum up, the same effort that has been put in Shadowheart, should be put in the other romances. In Astarion case, that means adding a couple of scenes/interactions in Act 3 after Cazador. Let him ask for an (expensive) present or clothes he likes. Let him ask for a portrait from the artist. Let him disappear one night to do who knows what and later find out what has he done now that he is free (I would say stealing Gale's underwear, but since many people have done that before, something else XD).
