Got it bro. When it's HK Harald it's not an exaggeration. When it's WB it's an exaggeration.
I don´t think Harald or Whitebeard could destroy the world or even close. Though I believe the way that Gaban and Imu were hyping him up, HK Harald with seal level 2 could have been the strongest character of that generation. He was simply a cuck, so the world didn´t notice him in the way they noticed WB, Kaido, Roger, Mihawk etc, but Rocks noticed and respected him/saw him as an equal, before he got a seal, and he also became known as the embodiment of fear or whatever.
Literally.
We had the actual final villain here, a mythical entity around for thousands of years, but it seems it's not enough.
You´re not wrong, but the problem is that Imu is the most bland and boring villain in the manga, and no one really wants to see him in action. Though if we´re being realistic, there´s zero chance anyone else becomes the main villain this arc, since the FB was all about Imu and the evil things he did, really the Gorosei and Garling didn´t even seem so unreasonable against Harald and the giants in the same way.