This is after he's kidnapped his old CO, falsified orders, hijacked Enterprise and set course for the forbidden world Talos IV.
Kirk said Spock was consider the best first officer in the fleet, perhaps that appraisal is by the people actually in the fleet
The example you sight is a display of personal loyalty, Spock risked the death sentence to come to the aid of a fallen comrade. He put his life on the line for the benefit of another.
It isn't a matter if Starfleet Command thinks him the best, the officers and crews of the hundreds of starships out there in the darkness admire him for what he did.