I wonder if they'd even care about ranks anymore after a certain length of time being stuck away from Starfleet. Janeway's talk about how we're "still Federation officers!!", which thankfully reduced a lot after the first couple seasons, always rang hollow to me. Voyager is clearly something like a privateer ship, and everyone just agrees to follow Janeway's orders because they have no idea else what to do, and she's the sort of person you'd probably want leading you home.
Tom's demotion and promotion really did amount to absolutely nothing. He's still just the same guy who has to do a 12 hour piloting shift followed immediately by a 12 hour sickbay shift in his relentless 24-hour sleep-free schedule, no matter what rank he ostensibly is.
Which was one of the fundamental flaws of the show. If it had been based in any kind of reality, nobody would give a crap about promotions, because there was no Starfleet or Federation to care about what rank you hold. You'd be too busy just trying to survive in an unknown area of space with little supplies and no other ships or starbases to offer assistance. But of course, VOY wasn't remotely based in any sort of reality.
I like Kim but not everyone gets promoted, that's just life. Wang was lucky. He was a young, new-ish actor and landed a long-term role as a bridge crewmember on a Star Trek show! There are worse gigs to have but he complains like he was a redshirt in TOS.
Wang was a lot luckier than you think, because they were going to fire him. If it wasn't for some stupid People article about the "100 sexiest actors" or whatnot, he would have been shitcanned. Instead, they fired Jennifer Lein.