By contrast, STID NuKirk felt to me like a step backwards, almost like his entire characterisation had been rewound back to that early bar fight scene from the first movie. I was disappointed with that aspect of STID.
To me (and this may just be the way I watched it) that was the point, Kirk is a natural leader who saved Earth and won the centre seat on Starfleets newest ship through bravado, out of the box thinking and a whole heap of luck.
The start of STID shows that while hes grown in his command hes gotten used to taking risks and them working out, looses his ship and shows he is the same guy from the bar fight as pointed out by Pike.
By the end of the movie he has lost his surrogate father along with watching a number of people die and almost gave into his desire for revenge, lost a number of people under his command, almost had his ship destroyed and then died saving it. For me the turning point is when he genuinely turns to his crew and says "Im sorry..." when he realises what he has done will likely get them all killed.
Hopefully the new writers will now show him as the Captain the Enterprise deserves now he has come from darkness and earnt his chair.