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I wonder if some of it isn't the influence of historical games on some of those themes and stories. If the idea of Arthur as a typical medieval knight doesn't quite square with the reality of the sub-Roman war chief and that puts people off in some way.
But anyway, medieval fantasy has been done to death.
You ever play Pendragon RPG? That's very much jousting, Vikings, high-fantasy type fun in an 'Arthurian' setting. One of my characters even jousted Lancelot and unhorsed him through some outrageous rolling!