I think part of the issue is Blizzard trying to have their cake and eat it too on this matter. It’s pretty telling that they want her to be complex, but like with everything they want to do, they don’t really manage to do it all that well or at least in a way that pleases everyone. Personally I think she’s a villain protagonist, a deeply evil character who would have zero remorse for killing children in the most horrifying way if it means to preserve her own skin and I think those moments where her fans consider to be objective proof that she is more anti-hero or even a tragic hero to me are just attempts by Blizzard to make her a bit more complex and not too boringly evil.
I won’t try to argue that these moments were just her lying to us or playing it all as an act though, instead I truly do think these moments were attempts by Blizzard to make her less one-dimensional, but at the same time I think that’s really just all they were and were not made to give some kind of hope that she was going to pull through as a true hero of the Horde or an anti-heroic character.
I have a whole separate opinion on why I think her character is a subject of controversy, but in my own opinion I think it has less to do with her consistency of writing and more to do with people’s desires for what they want Sylvanas to be. Most of it lies in headcanon whereas some of it is backed up at least by some of the writing, but overall I do think it boils down to that strong desire to want darker anti-heroic characters in a setting where the more idealistic noble hero is far more prevalent, and I do at least understand that on some level even if I personally feel Sylvanas was too far gone from even that trope as early as Cataclysm.
I’m sure others here will tell me I’m completely missing the point or didn’t address anything you said, but I’m not really here for an argument today, just here to show my owns thoughts on the matter.