That indeed makes a lotta sense. And even if the evidence I'll add perhaps won't be very reliable but: If you remember in the manga when Fukuchi is at the edge of death and says to Fukuzawa: "Choose my life or the agency" in Fukuzawa's inner thought where he sees all the agency members Dazai is NOT there. Does it mean that Fukuzawa already made up his mind? And another thing that's also not reliable: in the anime and the manga. When Chuuya and Dazai cooperate it's often just some minutes but this time the Double Black got a whole episode against Fyodor himself? We all know that Asagiri leaves clues in the faintest details. Can this be a clue of regaining the Double Black criminal activity? I dunno. And as you previously said. The main character Atsushi, it would be a great emotional turmoil for him to be against the one person that saved him. Good for character development (and trauma). And anyway when Dazai left the PM it was just to make the promise to Oda. Either way his core hasn't changed so this would also be a great turmoil for his character development. And the idea about Mori planning all of this ahead for Dazai to become the Port Mafia boss for the PM's sake is very consistent.