Controversial the Difference being Aliens in Naruto and Aliens in One Piece.

[Dettles]

The biggest difference between Aliens in Naruto and Aliens in One Piece is that in Naruto it came out of nowhere. at first the Moon was stated to be created by the Sage of Six Paths with the body of the 10 tails, and later retconned to be Aliens.

With One Piece the Moon has been in play since Skypiea. not just in Enel's Cover Story but as the "Endless Verse" in the arc itself. later we learn that there was an ancient civilization that lived there, and that it was the born place of the ancestors of the Bulkians, Shandorians, and Skypieans.

So it doesn't come out of nowhere.

 

[Welkin]

Well yeah that's why I've said from the beginning people are really weird about the whole "if Imu is an alien it's a rip from Naruto" thing

"Aliens" in the literal sense have been a thing since Skypiea. It's established that their race doesn't originate from the same planet as humans

Lunarians are also pretty much guaranteed to be aliens that decided to settle atop the Red Line

Imu being a member of one of the races from the moon would be perfectly normal