Plus, there are so many things in this movie that just weren't explained at all that it seems to me pretty easy to come up with your own explanations for it all anyway.
Let's say there was a planetary disaster, and the whole fleet was over there ferrying refugees, and it was such a complex operation that they called up most of the crews that were on leave on Earth while their ships had an overhaul. Skeleton crews were available for all the other ships, just supplemented by cadets (hence most cadets still being there in the amphitheater at the end), but the Enterprise was brand new, so they had no option but to give it to Pike and a crew of all cadets. Since there were no experienced officers, why not make Kirk first officer? Once that's established, the rest of the movie trots along merrily until the end, where Kirk is given command. But Starfleet just lost 6 ships with 6 experienced captains, and I can see Pike giving a speech to Starfleet that this guy needs to be a captain, that he just wouldn't fit in well if he weren't in charge. Sure, you have to posit some fairly loose promotional structure in that case, but I don't have any real trouble believing in a 23rd century aesthetic or trend that values performance above that kind of thing; the Starfleet presented in TOS wasn't exactly military-level discipline either, as I pointed out.
But now imagine a movie where they agonized over explaining all of that to the audience. Who would seriously give a fuck?
Let's say there was a planetary disaster, and the whole fleet was over there ferrying refugees, and it was such a complex operation that they called up most of the crews that were on leave on Earth while their ships had an overhaul. Skeleton crews were available for all the other ships, just supplemented by cadets (hence most cadets still being there in the amphitheater at the end), but the Enterprise was brand new, so they had no option but to give it to Pike and a crew of all cadets. Since there were no experienced officers, why not make Kirk first officer? Once that's established, the rest of the movie trots along merrily until the end, where Kirk is given command. But Starfleet just lost 6 ships with 6 experienced captains, and I can see Pike giving a speech to Starfleet that this guy needs to be a captain, that he just wouldn't fit in well if he weren't in charge. Sure, you have to posit some fairly loose promotional structure in that case, but I don't have any real trouble believing in a 23rd century aesthetic or trend that values performance above that kind of thing; the Starfleet presented in TOS wasn't exactly military-level discipline either, as I pointed out.
But now imagine a movie where they agonized over explaining all of that to the audience. Who would seriously give a fuck?