And Harald was being controlled by who? Usopp?
Imu has more control over Gunko but it's still only has a HK contract. She's limited by that. She's not Saturn. The Gorosei have abyss contracts.
You literally just aren't following the story bro. Harald wasn't being possessed like Gunko was. Harald himself said he was just being influenced, and we have a 1-1 comparison this chapter. Imu realizes Loki has the Nidhogg fruit this chapter, while not knowing who killed Harald in the flashback despite the fact that Loki used his fruit, because he's actually posessing Gunko directly.
Anything about his control being weaker is just headcanon for now, but either way, that would only be so Oda can make it even remotely feasible that Imu could lose here, since out of everyone on Elbaf, no one but Loki is canonically even capable of injuring him, let alone defeating him.
But yeah, despite the entire flashback of 20+chapters being about all the shit Imu has done, and Imu personally interacting with and seeing the characters in this chapter, he's going to have Shamrock randomly leave the mission he was on to return, to fight Luffy, lmfao.