The established Arabic poetic metres were systematically described in the discipline of ʿarūḍ associated with al-Khalīl ibn Aḥmad. Such codification allows poets and scholars to identify conventional patterns. Yet codifying a rule is not the same as exhausting every form of beautiful expression.
Balanced prose may fall outside recognized metres, just as a metrically correct poem may still be weak in meaning, diction, or suitability to its occasion. Metre is a literary device, not the sole measure of eloquence.
Qur’anic application: the quality of a verse should not be reduced to whether it conforms to one of al-Khalīl’s formal patterns.