Skills usually level by using them in litrpgs, which is how irl skill works, the difference being irl skill, there's usually a cap where you can't get much better at a noticeable rate without instruction, whereas with litrpgs that's often not considered. It is sometimes. But anyway, Skills leveling up, imo, is less a matter of skipping putting the effort into getting good, and more, skipping the need to be taught, or skipping learning the mechanical reasons why and just getting straight into the application. And tbf, some systems do require actual knowledge to get good, or the people in the world have noticed that just because someone has the Skill at a certain level, doesn't mean they're better, if they're up against someone with the Skill at the same level, but with a better utilization of the fundamental skill behind it.
The real sin is job/class levels universally increasing from killing things. Sometimes even Skills are guilty of this sin. A craftsman job/skill shouldn't level just cause you stabbed a goblin (or hit it with a Smith's hammer). You can explain it away sure, but it's unearned because it's rewarding you in an area that you weren't applying . Litrpgs, at their best, are a means to more directly reward character's effort over time, and specific notable achievements, and that isn't satisfying if the reward doesn't make sense relative to the achievement.
There are, notably different styles of litrpg, depending on the ideals of the author and what they are going for. There's a two main distinctions that I can think of. First, there's equal start, and inequal start. Pretty obvious, does everyone start with the same stats, skills, and class potential, or do some people get given special skills, classes, or stats at birth. And secondly, is the author trying to emphasize talent, or hardwork.
Inequal start is guilty of some of the more heinous wish fulfillment. Either the protagonist starts off special (almost always wish fulfillment), or doesn't. If they don't, then if wish fulfillment, they get ostracized for being weak, then they somehow get strong. In the case of 'hardwork' wish fulfillment, this often happens through what I've decided to call a 'hell arc' where they get stuck somewhere super dangerous, somehow don't die, and get out super powerful, and that time of suffering is used to 'justify' their power. Though sometimes, in that scenario it's actually a talent one, and it turns out that their 'weakest class/skill/whatever' had a secret application that nobody else had discovered or thought of and it's actually super stronkk and the protagonist was actually super talented all along! Very much the trashy wish fulfillment people think badly of litrpgs for.
Other times they just 'put in a lot of effort, more effort than anyone else because they were just relying on their op Skills!'. The trashy wish-fulfillment here is because it's feeding very directly on people who are jealous of talented people, don't think they put in any effort (tbf that's sometimes true), and it fills the fantasy of putting in a bunch of effort and way surpassing them. The problem is, they often apply that view of talent-no-effort to entire societies, as though no one ever tried hard work before, and all of the top people are made to be incompetent, and so the protagonist's wins feel unearned.
Sometimes, the 'put in a lot of effort' isn't the trashy kind of wish fulfillment, if it's handled well, if real genuine ingenuity is used on part of the protagonist, and they aren't getting their advantages because everyone else is dumb, but because they take on higher risks that others don't take, because they're desperate/determined and, yes, a bit lucky, but not outrageously so.
Equal-starts, or perhaps I should say, blank starts, have their pitfalls too. When the emphasis is more on talent, the protagonist gains skills super easily, or stumbles into some scenario that gives them an advantage, etc, when the author is focused on talent you generally know it's wish-fulfillment (I mean, all fantasy is wish fulfillment in a way, but, yah know). Hardwork variants can be just as bad if the protagonist is more powerful than their surroundings but it's not justified well, or, if all their accomplishments come from grinding. Just killing stuff, or doing repetitive tasks without actually applying any kind of knowledge or intellect to get better.
Training your Skills with a system shouldn't be, you do something a lot and the system makes you stronger, it should be, the system opens up new avenues of getting stronger, but to take advantage of them you have to apply both effort and knowledge, truly understand the what and how, in order to advance. That's usually the biggest pitfall of a hard-work based system.
Yes I noticed I got a little off topic. Shhh you didn't.
A skill is a formulaic process. So if the magic systems is governed by logic, there will be skills evidently.
