- competent or skilled in doing or using something.
Contrary to what you seem to think, skill can be judged in any field. Proficiency isn't some vague concept. I can look at a drawing of an arm and, YES, judge how skilled the artist is at drawing it. I can look at a cartoon and, YES, judge how proficient they are at stylizing, because you still need to know the fundamentals of shape, form, and the human body to make it look like a person without being realistic. Cartooning successfully is actually a very advanced skillset because it goes beyond just learning realism and fundamentals. It's being able to simplify a complicated thing into just a few lines.
There are many different definitions of success, and broadly it means you attained your goal, no matter what that may be. The success your talking about seems to be a common one: financial stability, doing it as a profession, maybe even fame. And yes, luck, marketing, and networking are HUGE in creating that sort of success. The best skilled artist that remains a hermit isn't going to be very successful in those terms, whereas a charming and genuine but mediocre artist can rise to fame with enough contacts.
But we're not talking about that, we are talking about objective skill, which DOES exist in art. The objectivity of the rules is exactly why I used language as an example. Art is used for human expression, yes. Your ability to convey that expression is the skill I'm talking about. You talk about the institution a lot like the hoity-toity art world is trying to hold you back by putting arbitrary rules on what's good and what isn't, or like it's adhering only to what was good in the past. Which, to an extent CAN be true at some schools or in the fine arts. They let their bias cloud their judgment. But that does not mean that there are no rules or that there shouldn't be any. I have had crappy teachers that graded based on their biases, but I've also had FANTASTIC teachers who promoted expression and graded based purely on the elements and principles I listed above.
For example: If technique wasn't important at all or couldn't be put on any kind of metric, artists wouldn't even be able to make a comic that could be understood. We wouldn't have a format--we wouldn't have panels, or camera angles. or speech bubbles that have to lead to the speaker. The fundamentals are in place so other people can understand what you're trying to say with your work.
Having systems in place is not bad. It is not an insult to anyone and isn't meant to hold someone back from doing what they love. It is there to give them the tools to express it and empower them.
Even in your cat example, what it means to people who look at it will vary depending on your portrayal. If you show the cat in a negative light--back arched, eyes glowing, maybe at night passing by a stranger in the middle of tripping, yes, your viewer is going to get the feeling that the black cat is the representation of bad luck. But if, instead, you show the cat dragging you away or nudging you awake in a potentially dangerous situation, then the cat would be seen as heroic by the viewer.
A regular picture of a black cat with no context? Just sitting on a white background? It's a cat. That's all your viewers will get out of it because that's all you communicated.
That's what I mean by skill in expression. An amateur may just draw the cat sitting and have their own story behind it, but because they don't have the skill to express it, it needs to be explained. Artists who are proficient in their craft would not need to explain.