We know very little about how Starfleet appoints it's captains.
Actually we know quite a bit because except for Kirk every command officer we've seen has been in his forties or fifties. That strongly suggests Starfleet tends to go with proven and tested officers.
TOS made mistakes and to some extent it gets a pass because much of it was being done on-the-fly and it wasn't trying to fit into a previously established continuity. But TOS often strived for a sense of credibility. And this is in direct contrast with ST09 and the Abramsverse which has no sense of credibility whatsoever. TOS was telling stories. ST09 is nothing but an amusement park ride.