As Thomas P. Campbell begins his third year at the helm of the cultural ocean liner known as the Metropolitan Museum of Art, he hears fewer comparisons between himself and his illustrious predecessor Philippe de Montebello, who served as director for 31 years. But the game of “Would Philippe Have ...?” remains irresistible at times, as it was in December, when Mr. Campbell seemed to be everywhere at Art Basel Miami Beach, the contemporary-art bacchanal that Mr. de Montebello virtually ignored.