Imu is weak.
I guess we have different understandings of weakness.
Sabo, injured, escapes from a room with 5 PK-level guys and one guy who is stronger than all of them combined.
Another one carries one of the 12 supreme grade blades.
All of them are mythical zoans being awakened. Is Kaido also awakened? But well, he has powerful Haki, so he's excused but again. One Gorosei carries one of the strongest blades, so his Haki is next level by default.
It's rather the contrast. Sabo fleeing from them is hype for Sabo.
one guy who is stronger than all of them combined.
Oda doesn't respect Imu to the point of not even providing a decent explanation for Sabo's escape...
You can cry all day
compare him, and lie about Kaido
2.) I didn't lie about Kaido. He failed to kill any significant character in Onigashima, he even failed to kill Speed.
but it won't change Imu's initial portrayal.
He is the head of the organisation which ruled over 800 years. Unlike Kaido, who thought Nika would beat him, Imu and Co actually managed to kill Nika. The reasons are still unknown but at least Imu is a step farther than Kaido. In his introduction, 5 top tiers bowed to him. He nearly killed Sabo with a single casual move and his cruelty even shocked the Gorosei who view humans no less than insects.