Yeah, silly decision to throw away all the tension and chemistry built up between the mastermind detective and the illusive killer to do a "well the mastermind detective actually raised two orphans to be mastermind-1 detectives and they kinda hate each other but now they're on the case" twist. Addiction to twists and/or "this is successful, I have to keep writing more of it for financial reasons" after already killing off L have to be the reasons.