But where did she lie about these things?
Nothing indicates there's anything wrong with Koltira.
And did Arthas not use Plague of Undeath and force ress people or something? Because you can see both aplenty in WotLK. Hell, he attempted to force ress the player.
The voices in the heads of Eternal Alliance Victims.
Everything Arthas did was his choice too, so you have no argument here.
The Deathlord had trouble with Liadrin. And how would they make Sylvanas a slave exactly? Not even Arthas could re-enslave her after Lich King first lost his grasp on her. Mage is going to get silences by her scream (and so are most other classes). Which can also break bones, particularly useful against Rogues I'd say, since Rogues are generally on the nimble side. There's no way the Hunter leader is going to best her in archery. Warrior is just going to hit a wall against the durability of her body alone. The only one standing a chance is the Paladin and they'll need a way to deal with her range advantage and precision of her arrows. Magical arrows most likely laced in all kinds of "pleasurable" poisons.