There is no difference also between the Vedic mantras and what is explained in the Purāṇas and Itihāsa. According to Śrīla Jīva Gosvāmī, it is mentioned in the Mādhyandina-śruti that all the Vedas, namely the Sāma, Atharva, Ṛg, Yajur, Purāṇas, Itihāsas, Upaniṣads, etc., are emanations from the breathing of the Supreme Being. The only difference is that the Vedic mantras are mostly begun with praṇava oṁkāra, and it requires some training to practice the metric pronunciation of the Vedic mantras. But that does not mean that Śrīmad-Bhāgavatam is of less importance than the Vedic mantras. On the contrary, it is the ripened fruit of all the Vedas, as stated before. Besides that, the most perfectly liberated soul, Śrīla Śukadeva Gosvāmī, is absorbed in the studies of the Bhāgavatam, although he is already self-realized. Śrīla Sūta Gosvāmī is following his footsteps, and therefore his position is not the least less important because he was not expert in chanting Vedic mantras with metric pronunciation, which depends more on practice than actual realization. Realization is more important than parrotlike chanting.
Ref >> Srila Prabhupada Vani.