Art has been and can be defined in many ways (obviously). Ad Reinhardt, one of the more interesting painters and thinkers in modern art, had this to say:
“The one object of fifty years of abstract art is to present art-as-art and as nothing else…making it…more absolute and more exclusive—non-objective, non-representational, non-figurative, non-imagist, non-expressionist, non-subjective.”
And he writes
"Tradition shows the artist what not to do."
I think there are parallels in Benjamin's focus on "authenticity" (as opposed to reproduction) and Reinhardt's repudiation of tradition, of copying, of art for any non art purpose. Reinhardt seems to have thought that his was the apex or perhaps the end of originality in art (not totally unlike Wittgenstein claiming, regarding his "Tractatus," that he had ended philosophy by solving all of its key problems.