I was speaking with disirdottir earlier, and we observed that Apollonian syncretists in Continental Celtic cultures tend to be associated almost exclusively with wells and springs…is this a knock-on effect of the Castalian Spring near Delphi, perhaps?
I also experienced this rather viscerally and directly with the first three members of the Tetrad++'s birth. They were very clearly there, then were named, then were understood; the other three emerged likewise, with their identifiable presence being perceived/experienced, then their names being identified, and then their understanding expanding and their myths unfolding.
That is interesting about the springs and wells. It could refer back to the Castalian Spring, or it could be a recognition of the symbolic value of springs as prophetic/intellective "sources", as we see in the Platonic terminology of pêgai, "fountains".
Your remarks about the order of the Tetrad++'s emergence are also quite on point. The etymologies in Plato's Cratylus are so rarely treated as "serious" by modern scholars, in part because I think that they don't conform to modern expectations about what would constitute a "reasonable" practice of naming, and yet I think that the account there resonates strongly with actual polytheistic experience of "discovering" Gods and then working to integrate Them into a worldview which is always already partly formed, and partly in process.
This integration necessarily lacks closure, unless closure is artificially imposed upon it. Hence we see divine names in the Cratylus not only having more than one interpretation, but the different interpretations of the names often track conceptual cleavages in the Hellenic worldview, such as between "Parmenidean" and "Heraclitean" approaches to ideality.