I'll comment on this:
To draw a division between administrative and defensive functions is not only logically unwarranted, but positively contradicted by the nature of those functions in an ancient Near Eastern context…Even if the former point were not the case, the Bible never sets out an “angelic taxonomy” where cherubs are placed into the single category of palace guards.
i) We can only work with the information at our disposal. The Bible doesn't have a whole lot to say about cherubim/seraphim. I wouldn't call it an argument from silence or ignorance to draw conclusions from the available evidence. Surely that's preferable to beliefs that aren't supported by the evidence.
ii) Moreover, isn't the divine council theory require a taxonomy of distinct angelic roles?
In the divine council in Israelite religion, Yahweh was the supreme authority over a divine bureaucracy that included a second tier of lesser elohim ("sons of God") and a third tier of malakim ('angels').
The Old Testament seems to distinguish angels—mere messengers—from the sons of God—the royal family; and in doing so it follows Ugarit, which had two tiers of gods: the sons of El, who ruled certain districts and provinces, and a larger group of lesser gods who acted as messengers and warriors.
Now, however, Bnonn is blending what he previously distinguished. In the quoted paragraph, he differentiates the administrative role of the top-tier angels from the defensive or revelatory role of lower-tier angels. So it looks like the original argument is undergoing ad hoc adjustments when challenged. But in that case, the distinctive assignments in the celestial bureaucracy or hierarchy seem to be arbitrary or interchangeable.
As for the "counterevidence":
i) Keep in mind that all these representations are anthropomorphic. It's not as if God is literally a white-haired man in royal vestments in a throne room surrounded by sentinels and courtiers. God projects that imagery into the minds of seers. So the question is the significance of the symbolism. I think the point is that God is holy, so that creatures ordinarily need to be shielded from direct contact or the Beatific Vision. The cherumbim/seraphim function as "hazard" signs. If you trespass on sacred space, it's like walking into a radioactive chamber.
That's a common theme in Scripture. It's not that God needs to be protected. Rather, creatures ordinarily need to be protected from God's incinerating holiness. I never suggested that their role is to protect God from trespassers, but to protect trespassers from God.
It's a graphic, anthropomorphic way to drive home a point about the relationship between sinners and God. And that's underscored by the literary device of even making the seraphim shield their eyes. In effect, the seraphim need to wear visors. Unfiltered vision of Yahweh is fatal. This is all rather picturesque.
ii) We need to distinguish between cherubic statuary and actual angels or visions thereof.
iii) Some OT theophanies take the form of a portable throne. A mobile, miniature throne-room. In that respect, cherubim/seraphim reprise their role as the outer vanguard to screen unwary eyes from seeing Yahweh directly. That's symbolism.
iv) I never suggested that angels are distinct from cherubim/seraphim. Rather, "angel" is a generic designation, whereas "cherub" or "seraph" is a specific designation. A special case or distinctive role for some angels.
Moreover, Heiser and Bnonn are the ones who propose an angelic hierarchy in which top-tier angels have different bureaucratic roles than second-tier angels, and vice versa.
v) As for Rev 4, that's different from, say, Isa 6, because the saints in heaven are holy in a way that Isaiah (or Moses, Exod 33) is not. They don't need the lead shielding to avoid a fatal dose of divine radiance.
The depictions are flexible because this is picturesque imagery that varies according to the context. It's not that angels naturally have wings or tetramorphic bodies.