If I understand what you are saying, Earth God is supposedly an ancient giant who later become a reference for someone to design a ship based on. Seems possible but I don't agree on Loki being Earth God, Loki already inherited the powers of God of War which he will soon inherits the title too, so giving him two Gods title is off Oda's standard.
We know Pluton was built in Water 7. To me it’s very likely that the same giants from Galley La who built the Noah were also involved in Pluton 800 years ago. And because of its destructive power they gave it the name of a god.
So you have:
Fishmen -> Eve -> Poseidon
Giants -> Adam -> Pluton
The prophecy about the two sovereigns meeting again clearly feels like it’s referring to Shirahoshi and Loki. I don’t really see any other alternative after everything that’s been set up in this arc.
If Pluton is the name of a god, by process of elimination I’d link it to the Earth God. If Shirahoshi is the reincarnation of Poseidon, the Sea God, then it would make sense for Loki to have some kind of connection to Pluton.
I think Loki’s eyes might hint at a dormant power. That power could be what makes him the Earth God and I don’t think that would contradict him also being the God of War. Being the God of War might simply mean wielding Ragnir. Loki has it because he was strong enough to be recognized by the hammer, but anyone strong enough could use it. I don’t see anything particularly special about that title for now. Meanwhile Shirahoshi, being the reincarnation of Poseidon, actually has special powers.
In Skypiea there was also the Vearth (earth) statue and it was clearly an ancient giant.