Akainu is several tiers below in hierarchy. Akainu's Bosses who bow down to Imu, tell Akainu to shut up.
The problem is, Akainu has no ambition. He is a dog blindly serving his superiors. If he had the ambition to separate the Marines from the WG and go against the Gorosei himself, you might've had a point.
@MarineHQ