You are missing the point lol, the Gorosei are stating who they believe to be capable of completing this mission.
“Instead of Imu, let’s send an Admiral” -> Gorosei ranking an Admiral relative to Imu
“Instead of an Admiral, we could send the five Gorosei” Gorosei again ranking one Admiral equal to five Gorosei
Of course Imu would arrogantly believe himself to be superior, do you know who we are talking about right now lmfao, this is literally the biggest god complex character in the whole world. This dude has the biggest ego on the planet.