Black Widow wins this one. She’s not limited to hand to hand combat. She’s got weapons training too. Plus, do you seriously see BW having any problem dispatching the likes of someone like Ricardo Diaz? She’d make mincemeat of him. But he beat Oliver to a pulp for a season and a half.
This Oliver Queen in name only probably would need to have copious amounts of plot armor to survive. Plus, in his best case scenario, she’d probably kick his tail for 21 episodes before he’d get one victory in the season finale. You know, because that’s the formula.