Celtic myth and arthurian romance

King Arthur was not an Englishman, but a Celtic warrior, according to Loomis, whose research into the background of the Arthurian legend reveals findings which are both illuminating and highly controversial. The author sees the vegetarian goddess as the prototype of many damsels in Arthurian romance, and Arthur's knights as the gods of sun and storm. If Loomis's arguments are accepted, where does this leave the historic Arthur?