Ziḥāfāt are recognized modifications of metrical feet permitted by particular rules of Arabic prosody. They show that even changes within poetry are evaluated against the conventions of a defined metrical system.
Those conventions should not automatically be imposed on every Qur’anic verse. The Qur’an has its own movement among long and short verses, pauses, sonic correspondences, and changes of presentation. Absence of a permitted poetic ziḥāf is not a defect of Qur’anic expression.
Different criteria: prosody asks whether a poet has kept within the chosen metre; interpretation also asks why speech pauses, continues, or changes form at a given point of meaning.