That is an interesting point. I always wondered how much Star fleet really appreciated Kirk. I mean if you reward him, its like giving a green light to officers to disobey orders. He stole a command cruiser. Yes he did save Earth but demoting him down was not really punishment, He wanted to be a Captain. He reluctantly accepted promotion in the first place.
It seems they are in a pickle, you want to reward him for his service but at the same time let people know that this kind of behavior will not be tolerated.