Marielle:

We have fundamentally different opinions and that is ok. I would rather kill Astarion, than let him ascend, as I would rather kill Shadowheart than let her kill the Nightsong.
Both turn into toxic characters imo and spawn Astarion even thanks you for stopping him, knowing, that he would have become Cazador 2.0. You see it differently and that is ok. For me discussions are not about "I'm right and you are wrong" I'm just interested in different viewpoints, a concept,that doesn't seem to be en vogue anymore nowadays.
No one was condescending to him in my game, Wyll made a tasteless joke once, but Astarion was well enough able to diffuse that on his own.
I don't know,what ending you gave seen,since there are several, but my Durge wasn't condescending and she asked,what he wanted to do. He said, he wants to see the world a bit, since he was bound to BG for so long. And it is implied, that they have great adventures together and exploring other ways to help Astarion with his spawn setbacks.
As for what I think is good - that he is free. Even with the spawn restrictions, he is still free to do and decide,what he wants. With the Ascension, he is basically tied to Mephisto, He made a devils deal. So he might be free now and if lucky for a long time, but when he dies, he will be Mephistos bitch. And Mephisto Likes to use souls for his experiments, so I see and fear a new cycle of abuse. That of course is speculation based on my DnF knowledge of Mephisto and devil deals in general. Maybe the 7000 victims buy the afterlife freedom for the one ascending too, I don't know. But neither does Tav/Durge or Astarion.
I personally must say, I find AA scenes pretty shocking. AA personally creeps me out and makes me highly uncomfortable. I wouldn't continue a relationship with AA, since I can't shake that creep feeling. He doesn't do anything shocking, though I would see him making you only a spawn after what he has told you about the restrictions of personal freedom for spawns as highly dangerous - that is my opinion, mind you,- , but it is more the way he talks, his body language.
In the end, we will never know,what would be better for the companions in the long run,since Larian won't make BG4 or a DLC. So at the moment it is one headcanon and opinion against the other.

As for Jaheira - she is awesome in BG3. Don't forget, it's a 100 years older and wiser Jaheira and I do think, they managed to catch her personality well.
And I honestly like Larian Mins more than BioWare Minsc. He was never a favourite of mine,but I can tolerate him way more here, than in the other games.

"We are all stories in the end. Just make it a good one."

Doctor Who