Unless I completely misunderstood the timeline, Star Trek (2009) has the following happen to Kirk:
- He goes to the Academy
- At the end of the Academy, he cheats on the Kobayashi Maru test
- He faces an inquiry over that, from Spock
- In the middle of that, Nero attacks Vulcan, and the entire Academy is shipped off to help
- Kirk (a cadet) is smuggled aboard the Enterprise by Bones
- Kirk gets promoted to First Officer under Captain Spock by Captain Pike, after the Narada defeats the Enterprise above Vulcan
- Kirk meets older Spock, who advises him to relieve the younger Spock of command due to emotional distress
- Kirk succeeds, and being acting First Officer, becomes acting Captain of the Enterprise
- They win
Immediately after, Pike relinquishes the Enterprise (according to Wiki, to be promoted to Rear Admiral), and Kirk gets promoted to be the Enterprise's Captain.
UH WHAT? Kirk just graduated from the Academy and has a grand total of one day of experience as an Officer!
How could he be made Captain of a flagship at that juncture, no matter how exemplary his conduct in that one day was?