I mean, the real reason Harry never got promoted was because the writers didn't want to waste time on Garrett Wang and his constant screwups. That was the whole reason he was gonna get killed in "Scorpion", so they could finally be rid of him.
Where the entire issue could have been handled in 20 seconds or so (Even only Janeway mentioning in an opening log he had been promoted would have been enough) without affecting anything else - except for mentioning him Lt. Kim from then on. In the end, they probably wasted more time to show that 'no we're NOT going to promote him!'.