I wonder how Law's Ope fruit would've helped him to control that thing. It's not the personality switch,
1) because Doffy mentioned the personality switch separately from the Ope's ability to give him control over the National Treasure ("..not to mention its personality transplant ability")
2) That would assume that the ability to summon Uranus, you would just need Imu's body and not his soul/spirit, when the one being able to wield an ancient weapon is "born", in Poseidon's case multiple times in form of a Mermaid, that means the power to summon Sea Kings leaves the body and is reborn in a new one, rather than being tied to the body itself.
@Sentinel @Playa4321 @Cinera so based on the "shadow" appearing and Doflamingo saying he could've gained control over the national treasure, it truly seems like Imu at most has the ability to call that entity. So that diminishes Imu's "godly" feat somewhat, as it's not Imu him or herself that can summon that power from his/her own body, but it's dependent on some outside force