Pyle was an illustrator, primarily of children's books -- this one was meant to be one. I first read it, and its three companion volumes, from my elementary school library, more than six decades ago. Pyle was considered to be an excellent artist, as well as a teacher of other well-known artists -- see the Wikipedia article on him. His most important pupil was probably N. C. Wyeth. The article says that Pyle's pirate book is largely responsible for the way current popular culture (such as the Pirates of the Caribbean series) shows pirates.
His idea of the world being somehow better during the time of King Arthur is interesting, and attractive, and it was probably one of the attractions of his series on Camelot, but I'm not sure that it is valid. The book which is the source of the quotation, and other books by Pyle, are available free from Project Gutenberg.
Thanks for reading.