Honestly I'm glad the illusion she had over Forsaken has been shattered, they have deifying and been little more than her lackeys for far too long. Yes they owed her for a lot, but gratitude can only go so far. She probably noticed she was losing her sway over them for a while, so I think she milked it as long as she could with this war. In times of crisis people are far less likely to turn away from authority figures or strive for changes in leadership, wanting stability in turbulent times.
So, Cataclysm Sylvanas definitely did want to strengthen the Forsaken as a race. She wanted to help herself by helping the Forsaken, there wasn’t some grand overarching two faced trickery going on there. The whole point of Edge of Night is to establish her new goal, after achieving the only thing she was “living” for, Arthas’s death, is making the Forsaken strong. For her sake, and for theirs. That’s the next thing for her to ruthlessly pursue, now that the Valkyr forced her to acknowledge that despite her initial view of them, something resembling concern and pride had grown for them, and thus she did have something to work towards on Azeroth besides simply avoiding death for herself.
Anyway, that was Cata writers, and this is BFA. Before the Storm definitely set up a simplistic bad guy Sylvanas/Forsaken relationship, because nuance is hard and Forsaken are actually mostly good guy care bears who are just tricked by Sylvanas who holds no real affection for them and just wants to control them 9_9. Look, I think having some Forsaken be Horde Loving Good Guys who deny Sylvanas is great, but I think they should be the exception rather than the rule.
My Cata Sylv headcanon of “YOU,,, ARE ALL,,, NOTHING” is once she knew it was time to peace out, she knew she had to sever ties with the Forsaken to save them potential grief from the Horde and Alliance once she was gone, and so they wouldn’t seek her out. So that’s why she made a big show double down of calling everyone nothing lol. But Cata Sylv is probably dead so rip slightly more interesting Sylvanas and Forsaken
