"I didn't want Varian to die and am only going to go to war because I can't trust his son to keep control" "I feel sad that Vol'jin died and didn't want to be Warchief. I'm proud to be Warchief and jealous of how well he ran the Horde" "I want to preserve the Forsaken that's why I nabbed Eyir" "I really want to take over Stormwind and gush about this in my own mind despite never having expressed such interest before and never wanting to do so after".
There's no amount of fanfiction that can glue pre-BTS Sylvanas, BTS Sylvanas and BFA Sylvanas together. Kosak didn't write EoN with the Jailor in mind, nor did anyone in Vanilla/Cataclysm write the laughable Orwellian state of BTS. In turn, Golden didn't write Sylvanas with the goal of killing as many people as possible or having planned Vol'jin and Varian's deaths. Hell, the writers in BFA didn't know if Sylvanas had told her dark rangers about her plans or not or whether she intended to ditch the Horde or not because they had to hastily rewrite the plot to fit the loyalist option.