Williams certainly has the type of style that will bother any welterweight, including Mayweather.

I've always said that when you have an elite speed/defense fighter like Mayweather, it's not the straight ahead body punchers that bother them, it's the long, rangy fighters with jabs.
To beat Williams, Floyd would have to constantly get inside Williams' reach to land punches. That's very tough to do. Floyd could beat Williams, but it will be tough to do.