How do we respond to someone who claims that the language of the Quran is not proof of its authenticity, citing Shakespeare's linguistic brilliance?

To establish someone's prophethood based on their eloquence, it is not sufficient for them merely to be eloquent and articulate. Rather, they must claim prophethood, challenge humanity with their eloquence, and humanity must be unable to counter them, in addition to fulfilling the conditions of prophethood. Eloquence alone does not signify a miracle or prophethood. The Holy Quran challenged humans, jinn, and mankind to produce anything like it, and none were able to do so. Allah supported the prophets with diverse miracles, circumstantial evidence, and laws of creation that affirm the truthfulness of their prophethood, such as the congruence of their message with the messages of previous prophets, their possession of high morals and absolute truthfulness, and the triumph of their call. This confirms that the ways of knowing prophethood are multiple and varied, and not limited to linguistic inimitability.