Boxing Evolution Theory would suggest Stevenson blows him away in the first 6 rounds that's roughly 80 years of sports science and improvement but then Walcott may very well outbox and KO him because of styles
Walcott isn’t straight on, he wouldn’t get caught by that left, which is the only weapon Stevenson has, whereas Walcott is versatile. All he’d have to look out for is that left, and he’d take that away with feints to make the timing difficult for Stevenson, he’d also himself off of the centre line etc and he’d knock Stevenson out.