One of the most fun aspects of revisiting TNG/DS9/VOY era Trek for me today is that, when I originally watched this stuff, I was a kid/teen/college student dreaming of working in TV/film and obsessively following the behind-the-scenes on this franchise. In the years since then I have been actually working in entertainment, and I've now witnessed this from the other side several times -- the axing of a series regular that is only ever publicly explained in the most blandly neutral of terms. And myself and other crew members would lurk in the online fan communities and be amused/intrigued by the speculation from the viewers of what really happened -- how some people were just completely off in outer space with totally ridiculous conclusions that they were 100% certain of, how others would guess exactly right, etc.
Anyway, my feeling, there is not a snowball's chance in hell the explanation that they just ran out of story for Kes is the truth. A firing that goes down like this is always because the decision makers do not like the actor in question. It probably really was precipitated by budget concerns, but in their minds, they are choosing to fire her because on set she is unprofessional/not good/difficult.
But, even though that’s what they truly believe, only some of the time is that reality, ESPECIALLY when it’s an attractive actress. All those old saws about how much harder it is for women in Hollywood are absolutely true: sometimes what gets the woman branded as difficult and unprofessional is that she has thoughts and ideas, isn’t sufficiently submissive, isn’t grateful enough for the job because she doesn’t understand how dime-a-dozen she is, etc. (See: McFadden, Gates)
Or a mix of the two. Since the male producers are already in this mindset of how replaceable pretty women are, it can take only minor missteps to sour the deal in a way that wouldn’t even register coming from male cast. I was skimming the Voyager section of The 50 Year Mission and was shocked by how awful Beltran described his own behavior as being. It sounds cliché, but if a woman had behaved that way, she would have been fired in a hot second.
Anyway, this is all a roundabout way of saying, I think the basic contours of this story are probably as we understand them. They had to cut someone for budget reasons, Lien and Wang were the two that were branded the most difficult, they had probably both behaved in ways that opened the door to being characterized that way (but just how bad it was, we’ll never really know -- and there's a good argument that a series regular can't make one mistake -- these shows are machines and you are paid the big bucks to do good work while also being a smooth cog in the machine -- really even a single incidence of lateness or not knowing lines should be considered inexcusable). I bet there were also "can we fire the only Asian?" talks, and people speculating that swapping white chick for white chick WOULD just be simpler that way, because that ethnic math ALWAYS comes up...
And probably some moron did weigh in with “we can’t fire him, look at this press he’s getting in People!” This is just the kind of thing some tertiary network executive would say, someone who really has no point and is looking for a way to involve themselves in decisions to justify their huge salary. Then you humor him with a bland pleasantry that says nothing ("I'm glad you brought that up") and move on.