I really think that Yoshida is meant to be a darker reflection of Aki and what his fate would have been if he was never forced to take care of Denji. Aki was a complete dick assaulting a teenager because he was convinced he was a bum, he would have continued being a pos if it weren’t for Denji. Yoshida has been forced into a similar situation but while Aki was forced to live in close proximity to Denji, Yoshida was kept at a distance. He was never meant to form attachments with Denji. So the small change Denji did have in him wasn’t enough to save him instead it was despair inducing showing him the life he could have lived as a regular teenager.