Ok, so, we know how the primordial sea is underneath Fontaine, and we also know, according to the Petrichor mission, that its ancient history is based on greek mythology.
That had led me to the assumption that, maybe, the primordial sea referenced a god/place talked about in greek myths. That would lead us to the god Pontus, who is a child of Gaia [the personification of the world (aka land)] (according to Hesiod) but also (according to Hyginus) a child of Aether.
Honestly, the fact that it is thought that he's a child of Aether would make things too confusing and doesn't contribute to what I want to explain. BUT Pontus is often represented accompanying the goddess Fortuna, the latin and persian goddess of Fate. (So I guess that's an interesting thing to know)
While I was in class, my Ancient History professor (I study archaeology) mentioned the primordial sea while discussing the "Epic of Gilgamesh" (good read), which leads us back to the Mesopotamian religion.
I'm not going to go into too much depth as I'm already writing this past my sleep schedule, but Tiamat is THE primordial sea. According to the epic "Enûma Elish" (haven't read it, but is apparently a good read), her and Abzû, the Groundwater, created the first generation of gods in Mesopotamia.
Could Abzû be referencing the Primordial One? The one who made the world habitable to humans, then created the first generation of gods (Celestia or possibly the first generation of "humans") did so through the Primordial sea (which we kinda know thanks to the Fontaine archon quest). This also means that modern fontainians weren't exactly humans because they didn't have the "consent" of the Primordial One.
I like to point out the obvious and talk about the correlations of everything. If a lot of this rant doesn't make sense, I'm tired.
Feel to point out any mistakes and add more information, I'd love to hear it. 😌