IMO it is not astonishing that different authors from different times, belonging to different religious groups, and supporting different interests make different and even contradicting statements about Hindu deities. One can expect such situation. Rather the opposite situation would be remarkable: If all authors would agree about the pantheon of Hindu deities.
According to the author of the Bhagavad Gita (BG) Krişhna proclaims: I am the highest deity. At the time of the BG, the classical Hinduism considers Krişhna an avatar of Vişņu. The BG is a cornerstone of Vaișņavism because it ascribes all power and might to their favorite deity Vişņu = Krişhna.
The Vedas are from the Vedic period of Hinduism which is much earlier and is shaped by quite a different social and religious structure. Here we have a series of different deities, most of them embodying some natural force or object. There are no devotees of special distinguished deities. Instead, according to the necessity of the sponsor the Brahmins perform a sacrifice to that god who is considered responsible.
The classical Hinduism has invented the Epics, the Puranas and the core writings of the different philosophical schools. In general, the Puranas are focused on one of the deities, mostly Vişņu or Śiva. The deity honored by a given Purana is elevated as the highest deity, and the other deities are reduced in rank.
Since about the 9th and 10th century CE, many smārtas have aligned
themselves with Śaṅkara’s Advaita Vedānta theology, at the same time
showing a tendency to elevate Śiva over the other four deities [Devi,
Ganeśa, Sūrya, Vişņu], in so far as they equate him with the
Advaitin‘s absolute brahman. (W. J. Johnson: Oxford Dictionary of
Hinduism. Oxford University Press 2009)
The authors of Hindu literature, notably of śruti and smŗti, express different opinions concerning their deities because they do not draw from the same single source. And that’s not astonishing: Religion is a parallel world in relation to our normal world. A parallel world created by human beings. And in that parallel world the rules that apply are different, contradictions are common.