It still doesn't make a lot of sense to me though. I figured being a "senior" officer meant that you'd had a lot of experience in the field and you were qualified for a position of some authority. It doesn't make much sense to me for an ensign to be made a senior officer right out of the academy. Especially someone as incompetent as Kim...or maybe I'm just biased against him because the actor can't act...
It never made "sense" to me either, and I chalk it up to bad writing (or, since it was a series decison, a bad series bible). There is no reason, even on a ship as small as Voyager, to make a green Ensign a department head. Absolutely no reason. I don't care how many enlisted crewmen there are, it doesn't make sense.
On that note, we saw more Enlisted crewman on Voyager than we did on any other show (which is remarkable, considering the ship only had 150 people to begin with!) and less senior officers. There were no Commanders on Voyager (unless you consider Chakotay a Commander, despite wearing Lt. Cmdr insignia) and very few if any Lieutenants.
Cmdr/Lt. Cmdr Chakotay
Lt. Cmdr Tuvok
Lt. j.g. Paris
Lt. j.g. Torres
The XO in Caretaker was Lt. Cmdr Cavit, he died while falling down the steps on the bridge
Lt. Stadi was the Senior helmsman, she was hot but died at her post. Also a Betazoid, so Tom's charms didn't work on her
The Doctor has no rank, the dead doctor was a Lt. Cmdr
There were various background characters throughout the show with various ranks. Interestingly enough, there were several "Lieutenants", including Joe Carey, that should have been department heads instead of Tom or B'Elanna (and certainly Harry). Ayala was seen with both Ensign and Lieutenant insignia, but I'm sure fans would prefer he was a Lieutenant. Most of those could probably be due to costume errors. It must have gotten boring in the costume department giving every background character an Ensign or no rank.
While we're talking about rank, it drove me nuts that in 7 years of Deep Space Nine, Bashir never got promoted to Lt. Cmdr. Nearly every other doctor we'd ever seen in Starfleet was at least a Lt. Cmdr (both Crusher and Pulaski were full Commanders), and he was supposed to be wicked smart.