your opinion is valid but just some things as an explanation....
* abuse is a cycle - at the beginning we only see the hyung during the honeymoon phase and over time, through flashbacks we see the tensions building and in the current timeline we see him explode. it’s textbook abuse.
* can’t think of suyeong actually accepting help from anyone so far, except for when mafia man essentially demanded suyeong work for him to pay off the debt. he never asked mafia man to tear apart the gym & hyung....
* suyeong was traumatized not only by the hyung’s violence but also that relationship in general and turned hypersexual as a result - it’s a real psychological reaction that I’ve seen people go through, the author isn’t pulling this out of her ass. that’s why he tries to sleep with mafia man when he gets confronted by his trauma.
* for the group of gangsters, suyeong landed a few good punches and then got his ass beat til he fainted... mafia mad had to take him to a doctor after to patch him
I agree with you about Minhyeok, he’s a shady but interesting character. However he also ticks a lot of those stereotypical cute/hot psycho sadist boxes which is pretty common as well.
For me, the writing seems generally consistent with the only unstable thing about Suyeong being his personality. That makes sense given at this point, he’s currently processing the abuse he’s been through.
We know that he hates being helped out of pity or treated like a victim, whether it’s his disability or growing up with an abusive dad. His moments of vulnerability have only started emerging because till recently, he’s been in denial/struggled to differentiate between his violent experiences in the boxing ring and Jisung.
Only after their last encounter do things change: When he sets off to save Jisung he has to fight his own body to push forward, then the fact he ends up freezing and then physically shaking in fear when he locks eyes with the man is a believable change in response for Suyeong. It shows him confronting the reality of their relationship admitting that when he thinks about Jisung’s violence “it hurts”.
His actions with Taeseung make sense given that he was lashing out and wanting to regain a sense of control after what Jisung had just done. They both went into it treating it as business rather than personal and were caught off guard by the fact they both got some deeper/more personal feelings of enjoyment out of it. It wasn’t a healthy way of coping, but it provided with Suyeong with some catharsis and since learning the truth Taeseung hasn’t treated him as a sex toy, he’s refused to have sex with Suyeong despite his requests.

what a mess, this story. they made jisung a violent lover so the gangster guy could become more tolerable. suyeong is a completely unstable character. he went from a boxing failure, to a guy the can beat a group of gangsters even with a bad leg to scared little slut. he didn't accepted help in the beginning of the story, but now he accepts anything real quickly.
there's this "i know you from somewhere" type of trope only for him to become the gangster's sex toy (so convenient) and it's that yaoi in which everyone likes men lol
the only think that will keep me here is the blonde dude. yes, he's interesting.
the trope "pay your father's debt"is old and overused but the story can still become good if they slow down the pace a little bit. it's up to the ch. 17, but i think it can still be promising.