Haha, oof, big ouch.
I mean, on the whole I like Anduin and his concept. He’s a rare character who has this effect on the people to help them move in a better direction.
That said, the whole point of Sylvanas’ character in BfA was that she was a.) wholly committed to the cause of the Jailer, b.) she was the darkness to contrast his light in the story.
Remember, this woman was so committed to the cause that she literally burned children alive. For her to “falter,” as she so put it, after talking to Anduin three or four times is a massive betrayal of not just her character but Anduin’s character as well.
To draw a comparison, what they did would be the same as if Garrosh suddenly decided that he was wrong and repentant after spending a bit of time with Anduin. It’s absurd.