Maybe their original appearance of Sun God looks like the fake Sun God, then 800 years ago, Joy Boy did something that made them call him Sun God 'Nika'. It's weird that they gave a new name to their Sun God, could be the name Nika in Japanese is called ニカ, ニ means 2, the second coming maybe? There could be other Gods come after Nika like Sanka, Yonka.
Dorry and Broggy is the legendary pirate crew that recognize Sun God Nika which means they follow the ideology of peace and freedom like what Joyboy stood for. However they got tangled in the old way from the first Sun God, self pride stuffs so they fight each other for 100 years to proof who is better.
The new giant pirate crew has totally reverted back to the old way of first Sun God, they don't even recognize the Sun God Nika.