
I like your analysis on this manhwa. Yes, I love the storytelling.
'The author gives us glimpses of what a good Yoon would look like'
If you don't mind, could please elaborate which part do you think Yoon showed some goodness.
My favorite part is when he patted sleeping Na-kyum in chapter 2. He had a concerned look.

He patted sleeping Nakyum on ch 2 is also one of my favorite, but all my friends have missed that. Hahaha when I told them about it, they all went back and was... "Whoaaa! He patted the painter like the painter is so soft."

I think Yoon showed potential in how he confronted the teacher. He sees right through the teacher. The Painter has a nasty habit of trusting the wrong people. The Painter didn't see the threat when the redhead brought him snacks. He doesn't seem able to read people or recognize the warning signs that they intend to harm him.
The Painter idolizes his teacher. He grew up in a brothel, yet can't recognize scum when he sees it. The owner of the brothel must've sheltered him a lot from the clientele that traffics those places for the Painter to end up so innocent.
Yoon grew up in a privileged world, but surrounded by vipers. It was eat or be eaten. Trust no one. Hurt them before they hurt you. That's how the world is. No one is nice without an agenda.
I think Yoon is baffled by the innocence and naiveté of the Painter. If you grow up among liars, a truly honest person would be confusing. You'd assume they're just a really good liar or a complete idiot.
Yoon can see as clear as day that the teacher is an absolute snake. He knows because they share that trait. The Painter is just a little bunny hopping around, trusting the vipers not to hurt him.
Yoon's is very intelligent and far more learned than the teacher and he knows how to play the game. If he used his talent for more than just destruction and getting off, he could be an incredible force for good. He could really save the Painter from that shady teacher.
I think Yoon wants to believe in goodness and I think he wants to stop being a monster, but he has no faith in that kind of thinking. Good people get devoured. That's the world to him. I think he felt nothing wrong with killing or destroying other people because they were all as rotten as him. But it's different with the Painter.
That's my take.

Thank you for the long reply. I always wonder what kind life Na-kyum had gone through in the brothel. Who knows he might meet his biological parents later in this story.

Get lost...We don't need a woke person here.

Why are you reading something you hate? That's silly. That's like complaining, "Ugh, these tropes about villains in movies are so overused and absurd!"
No one is making you read it. Instead you waste your time reading something just to whine and moan.
Stop being such a baby. There are plenty of non-yaoi stories out there that you can read since you clearly hate the genre so much.
Can I just say that this author is amazing? No only is her art skill through the roof but so is her storytelling. From such a simple premise she weaves in so much.
I mean it's basically, "Porn addict hires his favorite porn maker to make him exclusive porn, then falls for porn maker. Drama ensues," yet somehow it's great.
Really good storytellers don't play it safe. They don't avoid an idea because some fans might not like it. They go where the story is and tell the tale that readers really want to hear. The story that keeps us wanting more.
This is a story about one moral person trapped among very immoral people. Of course, the immoral will do immoral stuff. It'd be boring if they were moral people. For one thing, if Yoon was a moral person he'd not be keeping Na Kyum captive and he wouldn't be so desperate for the Painter's porn. Yoon was never written as a good guy anymore than Hannibal Lecter was written as good.
What we really want to see is if Yoon can be changed. If the Painter's influence can turn him from the rotten scum he is now into someone halfway human. The author gives us glimpses of what a good Yoon would look like, but it's ten steps backward and one step forward. We keep hoping he's not beyond redemption, but our hopes get dashed everytime so far.
When faced with a moral choice, Yoon chooses to be immoral. Yet slowly, we get a hint here and there that maybe he wants to rejoin humanity. That maybe he does want to be someone who is worthy of being loved. Unfortunately, yet again he smashes painter's face into the floor and our hopes of his redemption are once more put back on the shelf.
The author teases this hope out of us. This is what makes for masterful fiction. We keep hoping that maybe, just maybe, there is a light at the end of the tunnel.
We'll see.