Yeah, I like to say we found satan's mom, he's the Son of Dawn.
It's true that both lucifer (helel) and satan are titles so we don't get a real name, and both titles are highly overplayed in the churchianity wing of the real Jesus followers.
I can see your taking Anu-Enki-Enlil-Marduk and templating El-Shahar-Shalim-Helel over that (though Helel is the 8th-century title and the others are all very old Sumerian or Canaanite; Shahar as deity is rare enough we oddly have no older indications of any sons). But knowing the Isaiah tradition from his other poetry (some of the greatest of the millennium), he would be trying to rehabilitate "shahar" more than to build on an Enki-Marduk connection, even if that parallel is secondary in his mind. By the Isaiah II-III period (58:8), we have shachar as a positive feature of the messianic Day of Yahweh. I also found the Davidic "rehem mishchar", womb of the dawning (from shachar), in the messianic Ps. 110:3, which is definitely in Isaiah's mind; so the helel becomes a messianic claimant, an aspirant to the priest-king archetypal destiny.
Also by this time "son" is more metaphorical than regarded as genealogical among deities, i.e., helel is singularly representative of Venus-Dawn (Aphrodite, Astarte, Inanna). Seeing that Astarte was also later merged with Eos-Dawn, I'd venture to say that despite Shahar's masculine grammar (M) the word connects with more feminine contexts (F). So if Isaiah is familiar with Shahar weShalim, which is tenable, he could be invoking a connection between Astarte and helel that is representative rather than generative, and this would then be intended also to inform the character found in Job, the satan who is son of El (I don't generally say grandson as that concept is rarer than son's son).
So the thesis that El-Shahar(M)-Shalim is to be connected to Shahar-Helel to make a parallel history to Anu's family is not unmerited, but weaker than alternatives (which of course often coexist without being regarded as contradiction). I would certainly say the half-brother narrative as a recurring archetype is as significant as you note, and it makes one inquire of its original. But, at the same time, if I said El-Astarte?-Satan is also parallel to Elyon-Shahar(F)-Helel, that wouldn't be rejectable out of hand either.
Now the question then goes to what is the historian's intended narrative of all this. Either we're talking about history of some real family of humans or other sentients, or we're talking about categorization of deified concepts, with some overlap between the two. In the conceptual category it's not too troubling because concepts like Calf or Dawn are free to float around with multiple relationships. In the genealogical category we ultimately come to either dynasties or "watchers" and we have the harder problem that history is not allowed to contradict itself. In the overlap category I think we should consider deity names as we regard corporation names nowadays, namely they merge and split and take on or abandon meanings: so Marduk, if he is some spiritual entity, started out local but then may have taken on (some) connections that gave him rights in more names or titles, like satan. However, to me this doesn't rise to the level of plot hole in the Hebrew transmission, as I have such high standards for what would be irremediable holes that I can retcon most anything, and the ability to retcon later is often part of the intentional ambiguity of the originals.
I agree that people should talk about these things! I've noted that among Christians it's relegated to seminarians who then perceive that the Enlightenment covered it so exhaustively that there's nothing new to say or to "bore" the flock with. But unless we have robust understanding of the breadth of the sources (especially those taken as gospel), we fall prey to dropping one gospel for another hastily without validating either.
Add: Plus among my research tabs we have the pre-Davidic song "Aijeleth Shahar" (Ps. 22:1 KJV), dawn hind, which is the sun that reveals its horns (rays, wings) at dawn. This is certainly something Isaiah had seen preserved in Hezekiah's archives, which gives the relationship of Shamash-Utu intimate with Shahar, while Marduk's name comes from Utu. That might get us to Anu-Enki-Ninmah-Enlil-Marduk and templating El-Utu-Shahar(F)-Shalim-Helel over that (where Shahar is taken as the fertility goddess Ninmah wife of Enki). But it's all relative!
Yeah, I like to say we found satan's mom, he's the Son of Dawn.
It's true that both lucifer (helel) and satan are titles so we don't get a real name, and both titles are highly overplayed in the churchianity wing of the real Jesus followers.
I can see your taking Anu-Enki-Enlil-Marduk and templating El-Shahar-Shalim-Helel over that (though Helel is the 8th-century title and the others are all very old Sumerian or Canaanite; Shahar as deity is rare enough we oddly have no older indications of any sons). But knowing the Isaiah tradition from his other poetry (some of the greatest of the millennium), he would be trying to rehabilitate "shahar" more than to build on an Enki-Marduk connection, even if that parallel is secondary in his mind. By the Isaiah II-III period (58:8), we have shachar as a positive feature of the messianic Day of Yahweh. I also found the Davidic "rehem mishchar", womb of the dawning (from shachar), in the messianic Ps. 110:3, which is definitely in Isaiah's mind; so the helel becomes a messianic claimant, an aspirant to the priest-king archetypal destiny.
Also by this time "son" is more metaphorical than regarded as genealogical among deities, i.e., helel is singularly representative of Venus-Dawn (Aphrodite, Astarte, Inanna). Seeing that Astarte was also later merged with Eos-Dawn, I'd venture to say that despite Shahar's masculine grammar (M) the word connects with more feminine contexts (F). So if Isaiah is familiar with Shahar weShalim, which is tenable, he could be invoking a connection between Astarte and helel that is representative rather than generative, and this would then be intended also to inform the character found in Job, the satan who is son of El (I don't generally say grandson as that concept is rarer than son's son).
So the thesis that El-Shahar(M)-Shalim is to be connected to Shahar-Helel to make a parallel history to Anu's family is not unmerited, but weaker than alternatives (which of course often coexist without being regarded as contradiction). I would certainly say the half-brother narrative as a recurring archetype is as significant as you note, and it makes one inquire of its original. But, at the same time, if I said El-Astarte?-Satan is also parallel to Elyon-Shahar(F)-Helel, that wouldn't be rejectable out of hand either.
Now the question then goes to what is the historian's intended narrative of all this. Either we're talking about history of some real family of humans or other sentients, or we're talking about categorization of deified concepts, with some overlap between the two. In the conceptual category it's not too troubling because concepts like Calf or Dawn are free to float around with multiple relationships. In the genealogical category we ultimately come to either dynasties or "watchers" and we have the harder problem that history is not allowed to contradict itself. In the overlap category I think we should consider deity names as we regard corporation names nowadays, namely they merge and split and take on or abandon meanings: so Marduk, if he is some spiritual entity, started out local but then may have taken on (some) connections that gave him rights in more names or titles, like satan. However, to me this doesn't rise to the level of plot hole in the Hebrew transmission, as I have such high standards for what would be irremediable holes that I can retcon most anything, and the ability to retcon later is often part of the intentional ambiguity of the originals.
I agree that people should talk about these things! I've noted that among Christians it's relegated to seminarians who then perceive that the Enlightenment covered it so exhaustively that there's nothing new to say or to "bore" the flock with. But unless we have robust understanding of the breadth of the sources (especially those taken as gospel), we fall prey to dropping one gospel for another hastily without validating either.