Though lots of people know the basics of the mediaeval stories, not everyone knows that the oldest complete Arthurian story is the Welsh "Culhwch and Olwen." This story is thought to be essentially 11th century & even then based on earlier traditions.
In this story, Arthur is a folk hero, rather than a figure in the stories we know today. I think that you are right that the cultural and spiritual conflicts of the later stories are what makes them continue to resonate today.
