Sylvanas and willingly serving someone in the same sentence shouldn't be a thing. It doesn't compute. That's half of her character backstory.
But I'm sure Blizzard doesn't remember or care anymore, who knows maybe they'll surprise me. I still think the whole thing will probably backfire on N'zoth.
Yup, dumbest shit ever in terms of storytelling purposes. Especially for a character like Sylvanas who is supposedly intelligent/cunning. The quoted response just sounds like trying to find a reason to justify Sylvanas's completely selfish (and perhaps evil) action.
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She had some deal with Helya too right? And apparently Helya's alive and we haven't gotten much more than that yeah?