It seems to me that this conversation can go nowhere because you pre-suppose the Hebrew God is a man-made creation, and therefore, so are any developments in our understanding of Him. Whereas we believe that the Hebrew people were, in fact, specially chosen to bear a unique role in the drama of God's self revelation.
Can we prove that the Hebrew God is not man made, therefore, also the Trinity? I think we are moving into the question of "what is revelation exactly?" and "how does God make Himself known?"
It seems to me that you are looking for a "primitive simplicity", a moment where God's intrusion into the world is as bewildering as it is novel and pure, untouched by the contaminates of historical circumstance, culture, society or world view. I would argue that this is never the case, insofar as creation is already God's epiphany- self manifestation- insofar as creation is already a sacrament- a vehicle for His presence.
God created the world with an eye to the Incarnation, and I see Christianity as something like an idea taking flesh. The Word taking flesh, yes, but the Incarnation does not stop with the first Year of Our Lord. The image of God, He is also the image of man and so He, being made fleshly yet again (in an analogous way) in the bodies of His followers, He progresses through time and space, extending the border of His Body and causing all the streams of history and culture to genuflect at His passing and, like the three pagan Magi, to offer to Him whatever gifts that are their own.
It is, for us, not a real problem that the notion of a hierarchy of angelic hosts may have begun in Persia, or that the Great Flood is predated in Mesopotamian lore, or that Hebrews first encountered their God as a deity of the mountain, or that the Catholic Madonna is obviously anticipated in Isis and her son. For
[as] we prefer to say, and we think that Scripture bears us out in saying" that from the beginning the Moral Governor of the world has scattered the seeds of truth far and wide over its extent; that these have variously taken root, and grown up as in the wilderness, wild plants indeed but living...
I would suggest that your atheism is assisted by your looking for a "pure act of revelation" that presupposes no analogy between creation, human nature and the truths of God. This is the legacy of a certain Protestant theology which is bearing the fruit of unbelief.
Instead, we should see the role of the Christian Faith (with its Jewish antecedent) as a depository of the wheat of truth sprung up in a diverse manner across the earth; that the Logos became flesh because He, "
through whom all things were made", existed already in germ throughout what is His own; that Christ has become incarnate to "collect Himself", as it were, and all who have been in
corporated into Him.
As Blessed John Henry Newman says here:
The distinction between these two theories [as discussed above] is broad and obvious. The advocates of the one imply that Revelation was a single, entire, solitary act, or nearly so, introducing a certain message; whereas we, who maintain the other, consider that Divine teaching has been in fact, what the analogy of nature would lead us to expect, "at sundry times and in divers manners," various, complex, progressive, and supplemental of itself. We consider the Christian doctrine, when analysed, to appear, like the human frame, "fearfully and wonderfully made"; but they think it some one tenet or certain principles given out at one time in their fullness, without gradual accretion before Christ's coming or elucidation afterwards. They cast off all that they also find in Pharisee or heathen; we conceive that the Church, like Aaron's rod, devours the serpents of the magicians. They are ever hunting for a fabulous primitive simplicity; we repose in Catholic fullness.