And it's pretty much acknowledged two years later in Nightingale that if Kim had not been stranded in the Delta quadrant he would have been promoted a long time ago. Also in Warhead just a few episodes later it's pretty obvious that he is considered worthy of advancement.
If Voyager had done stories about the 'cabin fever' effect of isolation, Kim would have been the perfect character to spearhead that angle. Remember Kim pretty much joined Starfleet out of parental pressure. What if being isolated from that pressure made him second guess that and start to feel claustrophobic like I'm sure a sizable amount of the crew would have been?