It’s actually his character development!
Jounouchi fights a lot in the manga, and in the earlier manga especially. In addition to the above, we SEE him win a fight while holding the blade of a knife in his mouth, pointed at the back of his throat; he wins a fight while handcuffed to a serial killer wielding a chainsaw while holding a baby; he wins a fight (by knocking his opponent off a roof) after having shards of glass thrown in his eyes; he downs Bandit Keith with ONE sucker punch. Jounouchi, as he tells Keith after taking him down, is the best at fighting, bar none. There is a REASON that Yuugi, Honda, and Bakura restrained him when he tried to go after Kaiba in Duelist Kingdom, and it wasn’t for Jounouchi’s safety; it was for Kaiba’s.
But the thing is, particularly BEFORE meeting and befriending Yuugi, Jounouchi fought because he didn’t know how else to channel the emotional turmoil he was going through. Having to deal with an abusive, alcoholic father and shoulder the burden of his family’s finances since said abusive alcoholic father was unemployed and ALSO racked up gambling debts understandably filled Jounouchi with a lot of negative stress he didn’t have an outlet (or any real support, since his mother abandoned him there when he was 10) for. So he, regularly abused and living in poverty and debt, turned to gang activity and fighting. He left the gang after middle school, but continued fighting and trying to pick fights with others because, as he tells Yuugi during Death-T, he hated himself.
After befriending Yuugi, Jounouchi mostly fights to defend him (the song “Fear the Future” by Emma Blackery is a PERFECT Wishshipping song from Jounouchi’s perspective), but triggering his temper is still likely to cause him to jump to violence even if it’s not specifically to defend Yuugi (see: having to be held back from beating Kaiba’s ass in Duelist Kingdom). But this isn’t a healthy way to deal with negative feelings (or the emotional trauma of childhood/adolescent parental abuse). Jounouchi is the best at fighting, but he still sustains injuries, and how good does he REALLY feel after beating someone else into unconsciousness? He tells Yuugi that, when he returned the piece of the Millennium Puzzle he stole, “for the first time in my life, I kind of liked myself a little.” Beating people up didn’t make him feel better in the long term. Instead, it just contributed to his self-loathing.
But learning to play games like Duel Monsters DID help him in the long term. Jounouchi tells Yuugi right before the Ceremonial Duel that for him, becoming a “True Duelist” meant learning how to solve his problems in a better, healthier way. By the end of the series, Jounouchi has come to like himself far more than he did at the beginning. He’s gained a healthy outlet for his emotions, and learned better emotional regulation. Of course Duel Monsters isn’t therapy, and Jounouchi would still undoubtedly benefit from that as he still has clear struggles with self-worth even late into the series (ffs, in the manga, the entire reason he does Battle City is because he blames himself for Shizuka being too scared to remove her bandages, because he “couldn’t give her courage”), but it is a MUCH healthier coping mechanism than picking fights, even if he pretty much always won said fights.
So to tl;dr: Jounouchi solving conflicts via Duel Monsters instead of fists was specifically part of his character arc toward becoming a healthier person, and one he himself is proud of at the end of the series. He still can and will, if he HAS to, beat a motherfucker with his fists, but he has grown to a point where that’s usually not his first impulse/choice, and it’s really very beautiful.
