My scenario was that Harry was assigned as Voyager's second ranking ops officer. His superior, who was supposed to show him the ropes, was going to meet up with them after their milk run into the Badlands. So suddenly, Harry's what they've got, and he has to step up. Yes, the superior could have died instead, but Chakotay, B'Elanna, Tom, and the EMH all got their jobs that way. And this is just more ironic.
I sometimes wonder how the conversation around the planning table went, when they planned the character...
DEV 1: "So, who's going to have Data's job?"
DEV 2: "Ensign Harry Kim."
DEV 1: "Don't you mean Lieutenant Harry Kim?"
DEV 2: "No, Ensign. He's right out of the academy."
DEV 1: "What's a kid right out of the academy doing running a department on a starship? Shouldn't a brand new ensign have... I don't know, an ensign's job?"
DEV 2: "What do you mean?"
DEV 1: "Like on 'Lower Decks', an episode that aired just a few months ago. Taking orders, staying behind the scenes, and not knowing dick about anything."
DEV 2: "Oh, no. He's one of Janeway's senior officers."
DEV 1: "But he's NOT a senior officer. He's a newly minted ensign who was daydreaming in an exobiology classroom in San Francisco just a few days ago. That's about as junior as it gets."
DEV 2: "Yeah, so?"
DEV 1: "So... that makes no sense whatsoever."
DEV 2: "Yeah, well, those viewers are idiots. They won't know that."
DEV 1: "Why not just make him a lieutenant? That will work better, I think."
DEV 2: "Because someone's gotta be the ensign."
DEV 1: "Why?"
DEV 2: "They just do."
DEV 1: "Deep Space 9 never had an ensign."
DEV 2: "Doesn't matter. Someone's gotta be the ensign."
DEV 1: "All right, whatever... at least the character has room to develop... spread his wings... gain new experiences and learn new things. Grow from a wet behind the ears academy grad to a seasoned and competent officer. And of course, get a field promotion or two."
DEV 2: "Well, actually..."