I find it more annyoing how writers, intentionally or not, always sweep stuff like this under the rug. Apperently neither what happened in Stormheim nor Silithus mattered as the justification for upcoming war, it's all about how horrible Sylvanas is. I admit it's a bit extreme, but it's not strange at all that she wants to blight the shit out of Stormwind after genius Genn made his priority to kill her in the middle of apocalyptic demon invasion. In the end only thing that mattered was how Genn in his madman chase also by accident managed to save Eyir, which he didn't even care about. I mean from her pov, if he's willing to chase her in the middle of Legion invasion, what would he be willing to do when pocket nukes pop up all over the world? It makes sense that she feels like wiping out Alliance is the only way for them to be safe.
Then as cherry on top of misdirection, you have our treasure becoming High king, saying few nice words at a speech, some old lady frustrated by real world politics writing a book and it's all about how Sylvanas is beyond redemption and wants to murder poor humans for no reason. Ta-da!