What in the film says he has to graduate at the rank of ensign? Becuase Uhura managed to graduate at Lieutenant.
Nothing in the film says that. I am not disputing the ability to go straight to Lieutenant; I'm just saying that typically cadets go from the academy to Ensign. Going from Cadet to Captain is a farce.
None of that stops Trek '09 from being a badly written film, primarily as a vehicle to get Kirk to be the Captain and the status quo of TOS initialized before the end credits.