Starfleet Medical isn't just one building, but with transporters it can seem like one building. She's in charge of 100s of thousands of Doctor officers, nurse officers, orderlies and support staff, across the planet, and personally treats the admiralty. Sounds like a promotion to me.
A promotion in role doesn’t automatically mean a promotion in rank. The only medical admiral we know of is, I believe, McCoy.
The decision about B'Elanna was questionable at the time, given her run in with Lt. Carey. But, in the end, Janeway needed to promote a Maquis crewmember to a high role, just to keep Chakotay from being the "Token Maquis." Harry Kim, though, is another matter. Each department has a department head. Each department head has a rank they'll max out at. It's even in the dialogue in Caretaker when Janeway is talking to Paris. "All crew will report to Commander Chakotay. Even the Lieutenant assigned to conn." Lieutenant. Not ensign. So, in order to hold the conn position, ideally you should hold the rank of lieutenant, which Janeway granted Thomas Eugene Paris when giving him his field promotion. When leaving DS9, all key posts were filled. Lt. Commander Cavit was XO. Lt. Stadi was assigned to conn. Who knows what rank Rollins held, but he was in charge of Security/Tactical before Lt. Tuvok was recovered. Operations was held be ENSIGN Harry Kim. Not Lt. Kim, but ENSIGN Kim. Because a ship as small as Voyager didn't require a full Lt. (or even LT JG) to hold the position. Starfleet Command deemed that a lonely ensign by the name of Harold Kim was sufficient to man the Operations station. Maybe that's what Ops on Voyager maxed out at. Maybe if Kim had branched out and agreed to tutelage under the Doctor, or study under B'Elanna in engineering, or even pull extra work under Tuvok in tactical, Kim could have earned at least a Lt. JG rank. Slumming it in Ops doing the bare minimum didn't pass muster under Starfleet command. And pulling a couple of night shifts or commanding an alien craft in Nightengale didn't impress Janeway enough to warrant a promotion.
Again, the evidence doesn't support that claim. * In "Twisted", Janeway says to Harry that he has EXCEEDED all expectations. Not "doing the bare minimum" at all. * Harry aided in the design and construction of the Delta Flyer, and aided Seven in constructing her astrometrics lab. Clearly, when something needs building, he's the go-to guy. * There is flexibility in ranks: security can be run by either a lieutenant, or a lieutenant commander. And Tom remains at con despite being reduced to ensign. Ergo, Harry could certainly be at ops as a lieutenant. * Harry's duties made him among the "senior officers" on Voyager. We don't see Lt. Ayala or Lt. Carey there. Clearly, Harry is punching above his weight here. * If Troi, Geordi, Ogawa, Worf, Dax, Bashir, Sisko, Tuvok, and Tom can get promoted without changing jobs, so can Harry.
You forgot the big one... Sisko. And strictly speaking, so did Riker. Not on screen, of course, but Picard mentioned in "The Best of Both Worlds" that Shelby reminded him of a 'young Lt. Commander I took on as first officer.' He was XO of the Hood directly before joining the Enterprise. (Granted, it's moving from an older ship to the brand new Federation flagship, but the position was still the same.)
Deanna was already a commander, which is how she assumed command in Disaster, but to take command under normal circumstances you have to have passed the "bridge officers exam" which is about taking control of the bridge which she was not allowed to do, rather than take command of the entire ship because they couldn't prove anyone with a higher rank was still alive, which is what happened. Ensign Ro thought about killing her, and taking the ship. Deanna could feel that treachery, and was super cool about it. Medical ranks are parallel.
She held the rank of Lieutenant Commander for the whole show until the ending of season 7's "Thine Own Self". She was the highest rank in the "Disaster" scenario, which O'Brien rightly pointed out.
Have you seen Red Dwarf? Go watch Red Dwarf. (You're welcome.) The hero of the story a technician third class is sick of being bossed around by the asshole comic foil technician 2nd class, so the technician third class tries to get a promotion so the asshole with the higher rank stops being a prick and pushing him around. "how do you navigate around a black hole?" "I don't know." "How do you break when approaching the speed of light?" "I don't know." "You poor smeg head, if you don't know how to do those simple things, how on Io do you expect to pass the astro navigation exam?" "I don't. I'm going to pass the chefs exam. All I have to do is bake a soufflé, then I'm a technician first class, and I out rank you."
A smaller, older and potentially less capable ship with a smaller crew. IRL, moving from XO on one of the old Perry-class frigates or a modern LCS to an XO billet on a Tico or a Burke back in the day would be a lateral move in terms of role, but likely lead to a bump in grade.
Memory Alpha calls that place the Starfleet Centre on Earth. https://memory-alpha.fandom.com/wiki/Starfleet_Medical One building that is not the branch of service.
Reread the list. Sisko's on it. Commander to captain, no change in job. If him, why not Data (high rank)? And if Tom, why not Harry (lower rank)? It seems to me that being XO on a ship of 1000 would rank higher than XO on a ship of 150. And that if the CMO and Counselor on a ship of 1000 would have three pips on their collar, so should the second officer. Especially since he had repeatedly shown command chops, and was being held from the XO's slot by a peculiar situation (Riker's recalcitrance). Don't think I have access to it. Only streaming service I have is Paramount. And to determine whether Harry Kim's endless ensignhood was appropriate, better to look for evidence within the fandom than outside of it. Indeed. In the wet navy, a commander (or even LCDR) regularly serves as CO of a smaller ship. Having the CO of a ship always be a full captain is a unique aspect of Starfleet.
None required. EDIT: I could have also listed Wesley and Kira, but Kira wasn't Starfleet, and acting ensign isn't an actual rank. Though when Wes walked out of that turbolift in his red uniform at the end of Menage a Troi, it sure felt like a promotion!
Streaming? Guf-faw! This is ancient. You have to go see your weird uncle with a garage full of VCRs if you want to attack this series, unless you are the weird uncle with a garage full of VCRs. It started in 1988 on BBC2, and it's still going, but they have only made 74 episodes in 33 years. This is why Great Britain became Old Britain. No worries, I'm sure you can live without this series in your repertoire.
I'm quite weird, I'm an uncle, and I do in fact have multiple VCRs in my possession. But while I have a vast collection of videotapes, I don't have Red Dwarf. Far as I'm concerned, a red dwarf is a small star with a tiny habitable zone and a six trillion year lifespan.
Actually, RED DWARF is funny. It's on dvd. I have the set that has the entire series. At least, until they did BACK TO EARTH.
You make a good point, however on other ships we’ve seen conn officers ranking from cadet (!) to full commander (!!!). What’s special about voyager? the one exception I can think of being sisko, who was captain of the Defiant even while holding a tank of commander. Somethings to reinforce the idea that only captains can captain, though, are the temporary demotion Kirk gets in the first movie (but not in the second!) and the promotion Riker gets in BoBW but gets reverted in Family with no mention. At least Discovery let Saru hold his rank…
I think the only reason why Sisko was still a commander when bringing the Defiant was because it was still an experimental prototype. It had design flaws and issues until they were worked out and she proved herself that season. Then they were starting to produce Defiant class ships.