If Al-Ash'ari was the most حافظ (Hafiz - one who has memorized the entire Qur'an), would he be given precedence in leading the prayer (Imamah) or not?

If the innovator does not call to his innovation and does not stubbornly resist the truth, then there is no harm in his leading the prayer. Otherwise, someone else is more deserving than him, even if that person has memorized less.