Loki thinks he´s the sungod because he thinks he´s going to destroy the world and start ragnarok,not because he has some type of Nika fruit, which we know is all about having a silly design, rubber powers and transforming into white(we had people point this out in Egghead for example, Kuma, Saturn etc)Loki also thought Rocks, who had no devil fruit was Nika. Him eating the Elbaf fruit was completely accidental and not something he knew the lore of, but we know that serpents like creatures are worshipped on Skypia, and Loki has always been associated with animals,
@Shiroyru has a point that Loki could be the forrest god
And I hope you´re not seriously arguing that Rocks was looking for Loki and Luffys fruits, which are both somehow Nika fruits, when Rocks didn´t even know wtf Nika was, that just makes zero sense.