And what's most important, the concept or the skill in execution. I would argue that it's the concept.
And you would be wrong. You can sit engaged in mental Onanism all day but until you give those ideas a physical visual form... and a form that engages an audience... your thoughts are meaningless. Morandi's bottles and Cezannes apples are based upon the most mundane of "concepts". It is how they are realized that makes them worth something. Again, I would agree with Matisse's suggestion that there is no separation between thought and the creative process in the creation of a work of art. You fail to appreciate Lipking's painting in part because you fail to appreciate the nuances of the artist's touch, the subtleties of the decisions made concerning color, line, placement, etc... Such failure, in many ways, is owed to contemporary art theory that stresses words (theory/criticism/concepts) over the visual.
Oh... and concept is in no way valued over the visual in the majority of Modern art whether we are speaking of Picasso, Matisse. Bonnard, Beckmann, Klee, Kandinsky, DeKooning, Pollock, Johns, etc... Post-Aesthetic art begins with Duchamp but doesn't take off until the 1960s. Even then, it can in no way be claimed as the dominant direction in art from then until the present. Koons and Hirst and Emin are art stars because they are embraced by a super-wealthy class of collectors who see art as a means of proving their superior or more advanced taste... but they are in no way major figures to the larger body of artists, art collectors, and art lovers.