Heiser, Flusser and Lachs are millennia after the event.
The apocalyptic book of “Daniel” wasn’t finished until 164 BCE. The Maccabean writers refer to the auctorial presence 93 times as the son of man, ben-'adam. It never refers to the Messiah by that title, as it doesn’t in the other 14 OT references.
This does, but not as son of man;
Daniel 7:13–14
13 I saw in the visions of the night, and behold with the clouds of the heaven, one like a man (kibar 'anash) was coming, and he came up to the Ancient of Days [and who’s this? Unique to Daniel. = The Eternal, YHWH] and was brought before Him.
14 And He gave him dominion and glory and a kingdom, and all peoples, nations, and tongues shall serve him; his dominion is an eternal dominion, which will not be removed, and his kingdom is one which will not be destroyed.
that Jesus alluded to, deliberately segueing via son of man. His conversation with Caiaphas in Matthew 26 blurs that all the way to Son of God. Not God (the Son).
None of this has any bearing whatsoever on the economic Trinity.
If you have any links to any pre-Christian, BCE Jewish writings blurring the Shema, that would be of interest.
The son of man and son of God were, and remain, not coterminous with God the Son. Except in obsolete Greek thinking retained by the vast majority of Christians to this day, untouched by science and rationality.
PS However the Messianic Jews of Jesus’ time related the anciently highly evolved OT concept of an implicitly single Person God to the Messiah, they show no evidence whatsoever of proliferating entities in God, in making God complex. They were unitarian. To a man. Not that the concept could have existed on the spectrum of poly-heno-mono-theism.
The Persons of God are a much later, over 300 years, Greek Christian concept, derived from NT statements about God that nobody integrated at the time. Nobody thought about it. No Jew. How could they? They just unexaminably accepted the paradoxes, the Christian ones. The mystery. As the vast majority of Christians still do. Here.
The fact that Jesus was not simultaneously, concurrently, a Galilean carpenter and creator of eternal nature and transcendent being. Neither did the latter completely become the former. Neither can the former be unique as an incarnation of God. Incarnation is mediocre.
Who said what about who being what apart from those facts predicated on mediocre human incarnation is irrelevant.