Reality is the core of Vedas.
That the Reality is non dual is Advaita, qualified non dualism Visishtadvaita and Dualism is Dwaita.
Normally one does not find Brahman given more importance in the Puranas as each Purana extolls the virtues of the God on whose name the Purana is named.
Matsya Purana, Purana meant to extol the Virtues of Vishnu speaks of Brahman ordering and assigning jobs to the Trimurti.
What is interesting is that this chapter (Chapter 6) does not state that a particular God, Shiva, Vishnu as the embodiment of Brahman.
Instructions by Brahman.
Marry Lakshmi, destroy the wicked and protect the Righteous by taking Avatars.
Marry Parvati,be present in Holy places, bless people and perform Creation, Sustenance and Destruction.
Determine the fate of every one based on their Actions.
On this basis, Vishnu is present as Naranarayana in Badrinath,Madhava in Prayag,Sri Hari in Haridwar,Renganatha in Srirangam,Venkateswara in Tirupati,and as Krishna in Dwaraka.
Shiva is present as,
Somanatha in Saurashtra,Mallikarjuna in Srisailam,Mahakala in Ujjain,Rameswara in Sethu (Rameswaram) and as in all Dwadasa Kshetras as Jyotir Linga.
Parvati blesses as Sakthi
in 18 Sakthipeetas,
and as village deity in villages.