In Nightingale, Janeway laughed at Kim when he insisted that he deserved a promotion.
Okay this is what rank means... You can control more drones to save the day.
The higher you rank, the more drones there are, until you're Captain and every one is a Drone.
All the times Kim saved the day did he prove that he can organize and coordinate to victory a small team of crewmen like an ensign should be able to do, a small team of officers like a lieutenant should be able to do, a large team of officers like a commander should be able to do, or the full crew like the Captain should be able to do?
There was Futures End, Warhead and Nightingale, but for the most part, Kim did what he was told or saved the day by himself without proving any skills in commanding others.
Kim was Captain for a Month.
The Killing Game.
He capitulated like a punkass bitch when his only act should have been to blow up the ship.