These are, of course, the headcannons of the player, the player player character , but... Astarion Spawn, in the end, if you ask him to go look for a cure, he lights up with this idea. And here's the ritual, it's a terrible thing, someone says, but what if the new found method is even more terrible, and what? Will the PC, once again, persuade Astarion to stop? And the second time, I think Astarion will no longer obey, because it is really important for him to walk in the sun and other delights, because he repeats a couple of times in conversations: it would be nice to still get strength, but what is done is done, he is clearly upset, suppresses these feelings for the sake of Tav. In the epilogue without a relationship, or after a breakup, he says that now he owns his destiny, and when he finds a way to walk under the sun, now he will not miss it, nothing and no one will stop him. By the way, these are important words, the ritual was really important to him. By the way, a curious point, this is of course my subjective opinion, but Spawn Astarion is more honest without a relationship, but not in a relationship, while AAstarion is more honest in a relationship, and without them he is lying and trying to look cool, although he is lonely. Wow, we can conclude that Aastarion is better off in a relationship, and Spawn is better off without them, he does not need to adjust to anyone, and can do what he wants. I went through all possible options with Astarion in order to know the whole character, so I draw such conclusions based on both Spawn and Ascended. Ascension is great for Astarion, and staying spawn is forced by circumstances, so it's better for the player, or his PC, for the world, after all, but not for Astarion. I made such conclusions based on the passage with both spawn and ascended, as well as the ending with the subordination of the brain with Astarion, I like it too. Tav also became an Illithid, and I can say that AAstarion is more loyal to pc illithid. And of course, I will always choose ascension, because this is the best development for Astarion. Objectively, the ritual makes Astarion a better person, his character does not change, he is still the same Astarion, just a better version of himself. The soul is also with him. The fact that he lost his soul is just the empty conversations of his companions, which would once again prick us for choosing. And when he has everything he can wish for, the only thing that may be missing is a loved one next to him, and if that person is there, then Astarion is completely happy, as is Tav with him. There is no toxicity in their relationship. You know what I'm talking about... I like how Astarion reacts to the PC, that is, if we treat Astarion in a good way, then he is kind in return, and also, if Tav constantly gets on his nerves, compare with Casador, then he will be defiant in response. And it's so well done, so realistic, I like it. Therefore, if you and Astarion are on the same wavelength, then you will never see any toxicity. Tav and Astarion are doing well. And only one detail added with the sixth patch overshadows everything, it's Tav's face distorted with fear, but I'm sure that with the next big patch it will be fixed. It's not for the sake of argument, just my thoughts and reasoning. And sorry for my language, this is a Google translator.
Great points. My one quibble is that I do think you can interpret some toxicity into the Ascended relationship, even if you pick only complimentary responses. For example, the "don't stray too far line," if your headcanon is that Tav and Astarion are mutually enjoying a power play, then that line is fine. But a lot of people get skeeved out by that line, because they, or their character, wants to see the relationship as equal. Same with the, "You await my command" line. Some (like me) think it's perfect. Others don't like it and find it indicative of potential very controlling behavior.
BUT I do want to emphasize that even if there is toxicity, it doesn't make it an invalid choice for Astarion's story, nor does it let Unascended Astarion off the hook for some questionable behavior.