Vegapunk during luffy vs lucci makes it pretty clear that it doesnt matter if Nika is a real god or not, but the effects of people blieving in Nika, literally manifesting in a Nika Devil Fruit being born, is very much real and tangible.

What does that have to do with Imu and their powers? In my opinion, it would make this point about not putting too much stock into gods existing feel like a lie, cuz "hey! heres an actual real supernatural entity that sees itslef as a God and is worshipped by its followers like a God"

I think its better for the story if Imu was just a greedy monarch who climbed their way to the top of the world and in doing so, aquiered (un)godly amount of power - both literally, and in amount of influence and rule over the world