Oh you're so strong to put an unpopular opinion in a sea of... well, the 2nd cp lovers. I agree with you about Jintae 100% though haha I'm not enjoying the 2nd cp at all because of how they introduced him in the main story and I can't let go of it, so I felt like the odd one out. It could also be bec I lack empathy and can't understand his actions at all
But also, I feel like it's because I'm so sick and tired of problematic characters (I won't say anything toxic-levels because clearly a lot more characters in yaoi deserve that title) in stories after reading yaoi for more than 15+ yrs that I can't seem to enjoy them at all compared to the "bland and boring" main couple (based on popular opinion, and if not, then the loudest opinion in the comments section).
For real. I thought that he was going to be irredeemable at most but then after he got beaten up and after opening up to Dawun, he almost immediately had a switch up right then and there and it just pissed me off so bad. His past experiences shouldn't have been made to guarantee his awful behavior towards the MC at all.

Maybe I'm really just evil and downright awful but even with Jintae's entire struggle being laid out in the open, I still couldn't find it in me to like him as a character. I do think that he's a character who is written greatly; however, the way that he appeared first in the story stuck with me and I've never liked him since. I can appreciate the way that he was written but also dislike him – both can be true at the same time. I decided to read the side stories because I love Dawun but I was also kind of hoping that I'd change my mind about Jintae as well but to no avail. Then again, I've also always hated asshole characters getting redemption arcs so that could've been why I can't move past Jintae's awful past actions.