Kirk and Pike were the only ones to really get a promotion though. Scott was already in Starfleet and received a new job (not really a new rank, unless I'm mistaken), McCoy was a full MD before he joined Starfleet (in the real world, quite a few hospitals have Chiefs that are younger than McCoy -- it's about who can take command most efficiently), and Spock and Sulu were already done with the academy when we got to them. As for ranks while still in the academy, that's already been covered, so Uhura doesn't have much to worry about.
The only two people that seem off are Kirk's rather quick promotion -- and Chekov's newfound Wesley status.
Pike was already the captain and I could understand that this ONE mission was finally the one that pushed his accomplishments over the precipice to Admiraldom...
As far as Kirk was concerned, there were really 3 options.
1. Best Option: Promote everyone on the bridge one rank. (since everyone, except Uhura, participated directly in saving Earth)
2. Middle Ground: Promote everyone on the bridge one rank, but Kirk two ranks because it can be argues that Kirk contributed the most on the missions.
3. Worst Case: Ignore everyone else, promoted Kirk to CAPTAIN.
It doesn't matter that this is a reboot. It doesn't matter that JJ Kirk saved the Earth. Common sense demands that you don't promote an Ensign to Captain, a 7 rank jump, after one mission, after basically 3 days in command.