Is it permissible for the mosque's imam to recite the Qur'an aloud in prayer as if delivering a sermon, without tajwid?

Care must be taken in reciting the Qur’an as Allah commanded, "and recite the Qur'an with [proper] recitation." Scholars of recitation have gone to the extent of saying that adhering to all the principles of tajwid (Qur’anic phonetics and rules of recitation) is obligatory. This was affirmed by Ibn al-Jazari, who stated that adhering to tajwid is an absolute necessity, and whoever does not apply it is sinful. All rules of tajwid must be observed, especially those that alter the meaning and structure, which are obligatory, and those that beautify the pronunciation, which are recommended. Hidden errors in recitation (al-laḥn al-khafiyy) are not penalized. If the imam is good at articulating the letters and does not alter the meaning or structure, then there is no sin upon him, but it is better for him to be proficient. However, if he distorts the letters in their meaning and structure, then it is preferable for someone else to lead, unless that would lead to discord (fitnah). Reciting with a melodious, chanting style (tartil or tatrib) in performance is not obligatory; rather, it is a matter of scholarly disagreement, and affectation in recitation is blameworthy.