I think this view of all sociopaths reflects early clinical studies of sociopaths / evil individuals. There was evidently a 30 year gap between the initial studies conducted during WWII when the draft brought huge numbers of people, including a certain number of sociopaths / evil people into a controlled environment (the military) where they could be studied.
Anyways, the initial studies in the 1940s suggested that sociopaths ran the entire bell curve in regards to intelligence, cunning, personality skills etc.
But.... when the studies were resumed in the 1970s, the first sociopaths who were studied in depth were highly intelligent, cunning, and also possessed charming- though twisted personality skills. These traits then gradually became part of the definition of a 'sociopath'.
I think recent studies, however, have backed away from including these traits in the definition. Rather, sociopaths / evil people are just like ordinary people. Some are dimwitted, others are highly intelligent. Some are charming, others have limited personality skills. Likewise, though all sociopaths / evil people lie, some are far better at it than others.