That's what happens to someone who becomes a true vampire in dnd. The game tells you that in Act 1. There is a reason why ascending is the "bad" ending for Astarion's personal quest. Doesn't matter what kind of person he was before.
And I would also love him to be as OP as expected, but that would break the gameplay.
Is it morally questionable to choose his ascended quest line? Yes, without a doubt.
Am I going to choose it every damn time? You had better believe it! ??