However, Shiva and Brahma are still under the influence of karma, since they are created by Narayana, as declared in the Narayana Upanishad:
This is cherry-picking scriptural citations.
Svetasvatara Upanishad says otherwise.
Then we go to level II - whenever a scripture says God X is Brahman - "X" is a name of Vishnu or Vishnu is the Antaryami of X. This entire edifice rests on the deity-name "Narayana" and it has been proven at this site that Panini does not support the views of this sect about "Narayana" and that other gods are also called Narayana and equated to Brahman.
Obviously, only some Hindus are going to accept this.
Moreover, the Devi Bhagavatam is regarded as a Tamasic Purana, since it contradicts the supremacy of Sattvic Lord Vishnu, who is declared by the Vedas to be the supreme Brahman.
This site has discussed the "Tamasic Purana" thingy ad infinitum - it is in the eye of the beholder.
At least in the Rig Veda Vishnu has a birth and is subordinate to Indra.
Citations of Ramanuja are of importance only to his followers.
However, only Lord Vishnu can grant moksha, since he is the supreme Lord and beyond all sins:
Directly contradicted by Rig Veda "tryambakam Yajamahe" and Mahabharata (krishna himself says Siva grants Moksha).
This answer is presenting the views of one sect as the views of Hinduism, views that are hurtful to non-followers of the sect.
I don't want to enter into an argument with the poster of this answer - just asking him to add a caveat that he is presenting the views of his sect.