You are correct about the micro level, but you're ignoring the macro level. Their own lodgings and the books they have as mementos are as much a part of their former lives as the history of those lives themselves in the state of Lordaeron. You are ignoring the very clearly written dichotomy between the upper and undercities as symbolic of the divide between Lordaeronian and Forsaken and expressions thereof. Instrumental use of the Keep would be fine, militarily or otherwise, but leisure is not, because it'd be partaking in human activity in the places they used to as humans. This goes counter to the guards' statement to Parqual, and it is why Elsie is so terrified at the idea of leaving the Undercity to go to Lordaeron Keep, specifically. Compare and contrast Terenas' Tomb, Hallow's End and the other issues we've hashed out a million times already. Your perspective is, while still inconsistent, more nuanced but therein lies your error - the book is not nuanced. The line between former and new life is intended to be total in post-retcon Forsaken society. That's also why Sylvanas is so salty about Elsie changing her name back.
I agree with your reading about how the KotB saw their role, but Koltira intentionally making errors of judgment is identical in result to incompetence. In fact worse, because Koltira is not there in his capacity as a KotB, Thassarian even has to remind him of this - he's already sworn himself to the Horde and to Sylvanas specifically, calling her his Queen. Yet he still pulls all this stuff. You need to take into account Sylvanas (and the other Forsaken's) overall criticism of Koltira throughout the zone rather than just the final dialogue, since he was given a fair bit of leeway to fail before Sylvanas got tired and took over.It is Sylvanas' dialogue, after all - if she intended that then why not just come out and say it plainly as opposed to leaving it entirely to inference in this manner? She'd be fully justified in doing so, after all, as pretty much everyone is in agreement that Koltira had a few lapses in judgment in this scenario. Difficult to say if Koltira is incompetent or if he simply doesn't care overly about the faction conflict as both he and Thassarian were sent there to deal with the Scourge of Andorhal as representatives of their factions - once the Scourge is dealt with he and Thassarian opt not to fight, at least until a gaggle of Human farmers (not under Thassarian's orders as per the Alliance version of "The Battle Resumes!") decide to unilaterally break the truce and attack the Forsaken side of Andorhal. Sylvanas, hankering for a Val'kyr-themed weapons taste in any case (as per her standing orders to the Horde PC in the area in her disguise) had no interest in a truce and desired to attack the Alliance as soon as the Source presence was contained. I think it more likely the two Death Knights were there as Scourge specialists and once they did their part, had no interest in fighting each other until external circumstances on both their ends more or less forced Andoral into a resolution (in this case a Horde victory).
There's not much material to indicate that Sylvanas undertook any more special a treatment with some than others, in this particular context, mind. The choice given to Voss is the same as the one given the Rotbrains, the one to Amalia the same as Zelling. I agree that she's hampered by her own credos - her belief in allowing the Forsaken free will has repeatedly bit her in the ass given how many of them have betrayed her by this point, not just those like Zelling but Galen, Godfrey and so on. That the conclusion is not always the same is the point - Sylvanas doesn't intervene if the result is not the desired one (another soldier in her army who views the world as she does), she intervenes when there's a threat to her reign. That is what separates Derek somewhat, but doesn't quite go back to what she did pre-Cata in just having banshee possession as her go to. I disagree that Derek wasn't intended to internalize things, his mind was still his own and he controlled his body too, he references Sylvanas telling him 'lies' about Jaina's role in his father's death. It's the torture that's a form of cheating because it goes from mental manipulation to darker territory.I don't agree with that conclusion because, as we've seen and she's seen multiple times, they don't come to the same conclusions. I would agree that Sylvanas is hamstrung by her own credos (to which she at least maintains some credence to), but this whole arc is about how her hypocrisy grows with time and relative desperation - she takes more and more shortcuts with implicit covenant she has with the Forsaken, which tracks on from "Before the Storm" into BfA was things such as the raising of Derek Proudmoore. With Derek Sylvanas doesn't have the luxury of the "wait and see" approach she took with Voss, Galen, Zelling, or Stone - she needs a weapon and more than that she needs a "win," and she's willing to cheat to stay in the latter of the law while destroying its proverbial spirit. I don't think her intent was to have Derek be free-willed at all (hence his hanging in Dazar'alor and apparently being tortured by some kind of shadow energy), she wanted to hollow him out and make him the "bomb" that Derek himself references when he's freed by Baine and delivered to Jaina. That was her plan all along. Sylvanas is new to raising the Night Elves as Forsaken and probably not quite sure what tack to take with them to seduce them to her cause - she gives the appearance of feeling them out as she did with earlier such projects, and Delaryn would be a special case regardless (not unlike Voss and the others). Direct influence is for unique and special cases, not the rank and file of the Forsaken polity.
For reference, what was done with Derek isn't like what the Lich King does, but as I've spoken about earlier, it's arguably morally worse, owing precisely to the fact that Sylvanas has a personal investment and beliefs to prove through people whereas Arthas didn't. Being a spectator in your own body as you commit atrocities is one thing, being so broken down you do them of your own volition is worse.
Re: Golden and authorial intent. The intent of a rewrite I think is fairly clear, the lack of any reference to a different status quo speaks for itself, along with the first paragraph, but that goes beside the point. As does the Garrosh digression, admittedly.