I think the writers are intentionally writing her as an edgelord, she never talked in this way before. Suddenly she wants to “destroy hope” oh wait now it’s “destroy hope, which is life” so if it was old Sylvanas, she would say she needs everyone to die because…
An alive army couldn’t fight the old gods, because being alive you are vunerable to the old gods. So it has something to do with everyone having to die, and forming an Army to fight the old gods.
Except Sylvanas never bothers to tell anyone, the writers decide its better if we go through this entire convolulted xpac.