I would make a huge distinction between theater improvisation and film improvisation. There isn't much improvisation in film - there's virtually none. The people that theoretically could be good at this in a theater situation don't necessarily do this in a film in a way that will work, because it's much broader on a stage. But in a movie, it has to be real, and the characters have to look entirely real because it's being done as a faux documentary, so there are even fewer actors that can do that on film.
I was always the hero with no vices, reciting practically the same lines to the leading lady. The current crop of movie actors are less handicapped than the old ones. They are more human. The leading men of silent films were Adonises and Apollos. Today the hero can even take a poke at the leading lady. In my time a hero who hit the girl just once would have been out.