Hi Chemosh,
As I said, there is a long way from "Yhwh son of El" to the fourth Gospel, especially if we follow the scriptural path instead of the popular one.
Is Yhwh in Deutero-Isaiah still a son of El? I don't think so. The most obvious characteristic of Deutero-Isaiah is that Yhwh is the only god (actually, "God," probably for the very first time) and that other gods do not exist. To (over)simplify, it is one step "ahead" of henotheism, which had already merged the El and Yhwh traditions, then two steps ahead of polytheism where El and Yhwh were distinct.
The comparison with Deutero-Isaiah tells us one thing more: GJohn is dependent on the Greek Septuagint (LXX), which brings us several centuries further from the Hebrew Deutero-Isaiah in the history of thought, and in an already settled monotheistic context (again, at a scriptural level if not at a popular one). As has been repeatedly pointed out, the characteristic, absolute use of egô eimi is common to the LXX of Deutero-Isaiah and GJohn.
This is still the case in John 10:34: egô eipa theoi este is, exactly, the LXX wording (Psalm 81:6) -- and the part about "sons of the Most High" (huioi hupsistou) is not quoted. Moreover, I doubt any Greek-speaking Jewish reader of the LXX would still get any hint of the old polytheistic sense of `elyôn in hupsistos. Otoh I agree very much with you when you write:
the Jesus character does not claim to be the “I” in “I said you are gods.”
However I think this really makes sense, not directly from the old "El vs. Yhwh" pattern, but from the proto-Gnostic perspective in which theos is not limited to the original Divine (the speaker who says "I" is ho theos in Psalm 81:1 LXX) but extends to all the believers / elect, and a fortiori to the Revealer "whom the Father has sanctified and sent into the world" and who is, par excellence, huios tou theou. This argument, on the other hand, makes no sense at all to a closed, orthodox, monotheistic concept of "God". I agree this is, retrospectively, a fascinating resurgence of the old concept of "El" as "Father of the gods" which was dismissed by official Judaism. But that this resurgence could be deliberate on the part of the author of GJohn, or even understandable to him, is moot imo.