Both are action packed stories with focus on friendship instead of romance.
Weak hero is more focused on relationships and emotions, while maintaining great story telling and action bits while Black Knight focuses more on the main story and the main conflict. Black Knight doesn't develop the characters as much but there's still sense of comraderie and the general feeling of vindication is the same

Both are about gangs and the fight for what you believe is right, both are about friendship and focus on action with only hints of romance. Dokgo Rewind is about school gangs and bullying and High and Low is about the adult world of gangs. Dokgo Rewind has more social commentary.