Rather it is a divine miracle. The prophethood of every prophet was attested to by divine miracles. It is believed that the Qur'an is God's miracle confirming the prophethood of Mohammed. The Qur'an is the only inspired scripture that has come down to us intact as revealed to the prophet. It is not a human masterpiece but a divine miracle, where every letter and dot was revealed from heaven, with no difference between what was revealed and what we have in our hands.
Masterpieces are the work of humans.
Miracles are the work of God. A miracle, any miracle, is superior to the best of masterpieces. A masterpiece surpasses other works in one particular area. For example, a mastepiece of engineering does not necessarily have to have an aesthetic appeal. Or a masterpiece in art doesn't have to conform to engineering standards.