Reminder that Sylvanas grabbed a wolf and ripped its head off. She's pretty strong. And, as the Stormheim cinematic showed, she's very agile.
She might not beat Varian, but she'd probably beat Greymane in a real fight.
By the way, I can't recall it has been stated that Genn is as strong as Varian. If you have a source I'd appreciate a link.