I think Dempsey had enough punching power to hurt Wlad, despite the size difference. And Wlad showed he could be hurt by big punchers. But I'd favor Wlad to win this. Probably by stoppage.
Dempsey is size-wise comparable to Artur Beterbiev (what he walks around at). That's a really significant difference. And Wlad is no brutish mouth-breather, he could take pressure, move well, hit hard, defend skillfully. That said, I do think Dempsey had the power and movement to potentially make this interesting. Anyway, I'm taking Wlad by KO.