Antonyms for the word "most leading-edge" include outdated, antiquated, obsolete, old-fashioned, primitive, passe, traditional, archaic, and ancient. These words denote something that is old and no longer innovative, cutting edge, or up-to-date. They are the opposite of the latest and the most advanced technologically or intellectually. Such ideas, concepts, technologies, or practices belong to the past and have been surpassed by new, better, and more efficient ones. Therefore, it is important to keep up with the latest trends, breakthroughs, and improvements to stay competitive and relevant in today's fast-paced world.