I really don't know, i don't really watch footage that old. Because there not full fights, i like watching full fights and not highlights.

Jack Johnson was supposedly a very smart fighter, but im not sure how his style would of worked vs an aggressive fighter like Jack Dempsey.

I don't believe Jack Johnson moved very well like Gene Tunney ? which is the way to beat Jack Dempsey, so i'd say Jack Dempsey by KO.