A Question of Origin

Going back to Shakespeare, who is usually claimed as the greatest playwright ever born. But why is that? He hardly used any original plots! The plots were used and abused and in literacy terms, probably raped to death and then used a bit more. Is it the filling that made his work great? The composition? The new levels of character relationships, emotion, troubles and so on are what distinguish Shakespeare’s work? Just how important is it to be original? Is it merely enough to be able to form a pre-existent story mass into a beautiful final form? It is said that there are only seven archetypical stories that can be told. If it’s true is it pure delusion if we claim something to be original?