Yeah, I think it’s a misreading of events if someone thinks Sylvanas dominating Anduin and then saying “I will never serve” is somehow inconsistent. It’s just her character arc playing out.
Like, to lay this out end to end, we see Sylvanas convince the Jailer that she’s going to persuade Anduin to come onside and help them. Zovaal agrees to let her try it her way and makes her responsible for turning Anduin. But when she goes to talk to Anduin and explain why she’s allied with Zovaal (the machine of death is unfair and she wants to remake it into something better,) Anduin sees past all that to point out that Zovaal isn’t trustworthy. This is the first seed of doubt implanted in Sylvanas’ mind that maybe she’s backed the wrong horse. And it’s important to note here that this is the first time that Sylvanas has been straight up with anyone about why she’s doing what she’s doing. She thinks she’s going to convince Anduin by being honest with him but that doesn’t happen.
Next, Sylvanas asks Zovaal what he’s going to do about Denathrius’ capture and Zovaal tells her that Denathrius played his part so it won’t matter. This is the seed of doubt growing, that Zovaal doesn’t actually care about his allies and is just using them. On top of that, it’s where Zovaal forces the Anduin issue by giving Sylvanas Kingsmourne. Even when she brings the sword to Anduin, she thinks it’s his choice but again Anduin flips the script on her. The choice isn’t whether Anduin will willingly join, he won’t. The choice is: will Sylvanas dominate Anduin in order to pursue her goals? And obviously, Sylvanas chooses to do something terrible (dominate someone) for her percieved greater good (remaking the machine of death into something fair.)
After this, in the battle of Ardenweald, Sylvanas learns Tyrande murdered Nathanos. This is more doubt, it’s ramping up, because she realizes that Zovaal didn’t tell her about Nathanos’ death and allow her to reunite with him (like he predicted he would at the end of BFA.) These are the warning signs that she refuses to acknowledge, the red flags she can’t see because she’s so close to the goal that will make everything worth it.
And that culminates in the Sanctum of Domination raid where she successfully holds the players and Jaina, Thrall and Bolvar at bay long enough for the Jailer to complete his ritual. And when he does, standing on the precipice of completing his eons old goal, he tells Sylvanas that he wants to remake a reality where everyone serves him. This is the moment those seeds of doubt blossom and Sylvanas realizes she’s been played. Anduin was right. From the very first minutes he was captured, Anduin was right. And it’s this moment where she turns on the Jailer, even if the effort is ultimately futile, saying “I will never serve.” And obviously, over the course of 9.2, Sylvanas is now motivated to undo the harm that she’s caused, free Anduin from his domination and stop the Jailer.
So, it’s not inconsistent writing for Sylvanas to dominate Anduin and then say “I will never serve.” All the narrative tension in Sylvanas’ choice to dominate Anduin relies specifically on the fact that Sylvanas isn’t comfortable with dominating someone, but she’s willing to do terrible things to accomplish the greater good. And her realization in “I will never serve” includes a realization that she made a greivous mistake in dominating Anduin, which is why in the cinematic, she’s the one shouting his name and running forward. She’s the one that made the choice to put him in that position in the first place.