I think it is not as bad as with Naruto. Imu still falls within the established framework. Ancient guy due to immortality, but his power is still based on a Devil Fruit, he is introduced with an apparent weakness spilling blood upon arrival, being tormented by Joyboy and Davy Jones' incarnations as per his own words, rules for 800 years but can't achieve his perfect world yet.
It's not like with Naruto, where suddenly a planetary level alien appears that can instantly neg diff the entire world and one power creep replaces the next.
The power level difference between Juubi Jinchuriki and even more so Kaguya and the next big shots (Hashirama) is astronomical, but much less so with Imu compared to the Yonko.
The fact ancient weapons play a crucial role already shows that power levels won't be creeped out entirely, or else Imu's and Luffy's power level alone would be enough.