They had a measly two hours to introduce Kirk, and everyone else, and do a whole action plotline involving a grumpy Romulan miner, plus Old Spock and time travel/alt-u stuff...so no wonder Kirk's development got short shrift.
Kirk is young and unformed. His overt personality might be nothing more than a defensive shield, and his true self is yet to emerge. The upcoming movie is where that change will start to happen, if it's in the cards. Kirk does need development, but it's impossible to judge the process now.
This is all part of the frustration of Star Trek not being on TV, where character development could happen much faster. Two hours every three years is maddeningly slow and is just more evidence that Star Trek is too complex to be relegated to the movie format alone. Too much potential has to go to waste.