Exactly, this is one of the most realistic depictions of character development for someone that has literal mountains of past trauma as JK does. He’s only ever been rewarded for his violence or taught that violence is okay of course he’s gonna need to figure out that’s not how other people actually operate. People want JK to just go from jerk to prince in three chapters but I personally much rather him figure out it’s him that’s causing KD to suffer and learn from it than him to continuously beat KD mentally and physically. People don’t change unless they’re smacked in the face with the consequences. JK is being hit in the face with it now, even if he doesn’t realize it’s his fault yet.
The story isn’t about JK magically becoming someone that KD can love it’s about the growth in between and I think the author is nailing that aspect well.
His growth is slow but on one hand, he has ZERO idea what it's like to treat someone kind and with love. He would he? He went from a crazy abusive dad to a grumpy ass trainer and violence never stopped even if he started getting paid for it. On the other hand, he's going to have to go through a huge amount of self reflection and a mountain of aha moments to come close to what Dan needs. His brain and his heart need to have a meeting to get on the right track.