I don't think we're on the same wavelength here.
I am stepping out of the narrative to discuss creative intent and player perception at different times in Warcraft history, while you are doubling down on the current narrative and trying to make it work retroactively. Afrasiabi "confirming" it (I thought he went back on it, but won't die on this hill) doesn't mean it's not a retcon. And keep in mind there's a huge difference between her ordering the creation of the Blight and a surprise attack on Arthas at the Wrathgate, possibly unbeknownst to the Horde (which I don't think anyone is contesting?), and her ordering a betrayal on the Alliance and Horde forces there.
I get that you have a huge Sylvanas hate boner right now and you're... stroking it while it's hot, but you might want to consider that a retcon can just as easily turn against you. If they give Sylvanas a Kerrigan story and claim that was the plan all along and you misread the signs, will you be ready to accept it? Asking hypothetically.
She specifically didn't because barrels of Blight were wasted on friendly troops, and afterwards there was nobody to take advantage of Arthas's weakness. She literally had nothing to gain from the Wrathgate going the way it did.
I am speaking of my experience playing through Warcraft III (multiple times over) when I was a teen, and the way it informed my attitude towards Sylvanas through most of WoW. Again, you are reducing everything to the latest narrative... though I don't see how Sylvanas's recent atrocities could possibly whitewash Garithos.
He was using her too and was going to break their deal just as easily, he was just too stupid and too arrogant to see it turned against him.
The irony in that story line was that he was about to genocide the Blood Elves for accepting help from the Naga, but he had no problem using a Banshee and her Undead army to fight for him. He was a racist, dimwitted hypocrite, hated even by the dwarven troops he
didn't try to execute. Blizzard is turning every other Horde character into a villain, but would never make another Alliance character like this... which is ironic, because judging by this forum and how many ally players direct hatred and discrimination at their own faction (they hate and mock Gnomes and Mechagnomes, hate Kul'Tirans because they are fat, hate pretty much everything they get, take everything for granted and whine all the time), you'd think they'd feel right at home among some dumb xenophobic shitheads.