Well, my thought on that would coincide with the fact that Imu does not recognize Loki's power. Think about it.
- If the Sun God was whole thousands of years ago in the first world, Imu was not alive then, but we assume his "power" was (one of the other Gods). The Sun God apparently perishes, and possibly split into two. In the first world, these two beings do not meet again
- Fast forward to the 2nd era. Joyboy eats 1 half of the Sun God's fruit, the liberator side. It sounds to me, just based on past dialogue that Elbaph was a literal king in this era, given he has a D. Initial. If Elbaph did not eat the fruit Loki has, then it would imply they did not meet again in this era. And thus, Imu has no recollection of the Destroyer Half of the Sun God.
- Now the 3rd era is happening. Shanks apparently gets Loki back to Elbaph (physically or by convincing who knows). This is after the fact that Shanks already knew Luffy ate Nika's fruit, like Joyboy, and Loki had already eaten said fruit in this era. You can see how Shanks is basically orchestrating those 2 to meet, especially since he went to visit Loki right before Luffy got there and we dont know what was said yet.
Imo this is what the Harley is talking about now.
And fwiw, I think Imu is the Earth God again, simply because of the fact that his Gorosei all are planets and so are the ancient weapons. We are back to the idea of Geocentricity (Imu/Earth) vs Heliocentricity (Luffy/Sun) and I think the idea of this is still valid.