Still, she betrayed him while he didn't do anything wrong towards Sylvanas and her people. We will never know if he would have betrayed her. Right now, you can't deny that Sylvanas started aggressions towards humanity, not the other way arround. There was never a moment were Sylvanas tried to establish peace with the Humans. Thrall, by inviting the Forsaken into the Horde and never controlling her people and Jaina, by supporting the Alliance war against the Horde, did a shitty job, but at least they tried.
That Dalaran should be neutral is shit to begin with. It was a Human Kingdom of the Alliance. And it sucks always having Alliance stuff turned neutral.