I don't know if i completly agree but the we already have concept of gods being introduced like sun god nika , so its only logical we'll have human devils
I think Oda took Inspirations from two things
1. He wanted to create Fusion Characters similar to Dragon Ball Z (Oda worships Dragon Ball)
2. He inspired it from German Literature "Faust"
The idea is very simple, just like Oda wanted to create Gods & people who get Inspired by them, he also wanted to create Devils & what do people do with Devils? They make Deals with them
The saying "Make a Deal with the Devil" originates from Legend of Faust
And without getting into more details, i believe Imu was designed based on this:
In other words, Imu is a Dual Person, a Woman & a Devilish Man in One Body
And there is a Solid Argument for it:
Imu in Kanji is イム
Eve is イブ & Adam is アダム
So basically
イブ + アダ
ム =
イム
Imu is named after Eve + Adam (Imagine like they are named Evdam)
And when written in Katakana, Imu's Name means "Buddha" which also translated to "Enlighted or Awakened One"
Which again is a reference to Clairvoyance or Ascended Humans
Personally, i believe Imu we saw looking at Giant Straw Hat wasn't in Real World, he was in Other World where Devils exist
(The Man-Controlled Afterlife, that's why it's Cold just like Brook described the Afterlife he went to & came back from thanks to his DF)