Who?
His opinion makes a lot of assumptions about the enterprises importance that bear no relevance to the alternative timeline.
In TOS the enterprise was not the flagship, it was one of 12 identical ships, important to the federation, but not irreplaceable.
The ship became legendary because of the actions of Kirk and his crew on that five year mission, and the missions that followed, enough to make sure the name carried on in other ships, although either they took care of the B for a very long time, or there was a significant gap between B and C, there definitely was between C and D.
In 2009 there was no mention of the enterprise being the flagship then either, and it didn't have any history because it had only just been launched.
There were cadets on board because the ship was not expected to be taken into battle, much like the similar situation in star trek II.
At the end of the film Kirk was willing to spare the life of the man who killed his own father in the name of peace and the greater good, to suggest that this is the same cocky Kirk from the start of the film seems to be the mark of a person not really paying attention to the film.
And if Kirk is not acting like the Kirk we know, maybe because the Kirk we know had a living caring father, not some abusive step father banging his mother to get closer to his dads collection of antiques.