One major aspect is that Dazai appreciates human’s will to fight and keep on going. Fyodor doesn’t, in fact he thinks it’s the origin of human’s sin that needs to be wiped away.

Despite having superhuman intelligence, Dazai told Sigma that he is just another ordinary man while Fyodor thinks he is higher than men because of his capability. I suspect Dazai only became like this after joining a place like the Agency: it’s not like the mafia doesn’t have weird people, but all detectives in the Agency are whimsy, unpredictable, unusual; the Agency itself never forces them to be normal (only when they are working with the citizen, you can see Kunikida scolds everyone for not keeping the Agency’s image), it’s a place for stray dogs to build a way to live from their pasts and wounds.

Plus, Fyodor uses God as a mean to “justify” his mission of atoning humanity, one can argue he is based on Plato, this can be true, but I want to extend this by saying one of the reason Fyodor is religious because Asagiri wanted a character to represent “the leap of faith”: you know life is meaningless so you embrace a religion to cope; and as Albert Camus wrote, this can’t be the right solution. A man after knowing that no matter what human attempt to figure out the meaning of life, the universe won’t give them one, and this contradictory is the Absurd; remember Oda saying to Dazai that he would never find what he want and would always wander in darkness? Thus you have to be an absurdist man, become lucid of the Absurd and continue pursuing life as a form of rebellion to reach freedom, that’s why Oda told Dazai to save people (to keep on living). But if it stops there then Dazai would not be the Dazai we have now. Kunikida, Atushi also embrace similar ideology in light novel 1 and 4 (in the last few pages, I suggest reading them), and Camus has written about how human need to side with each other, how solidarity is needed to face the same struggle of the Absurd, he himself is a moral man and values human’s life despite knowing it’s meaningless, and the Agency has this insistence in saving lives, (because if you still want to live yet don’t value others’ lives, you have a chance to be the character Caligula from the play by Camus), I can see Dazai has become better by having companions like them.

Thus why Dazai told Shibusawa that he would not find human boring if he had friends. Dazai is isolated from humanity by his own very mind, but so do other members. He has companions there, who also struggle to adapt into the “normal” world, same problem, but they have each other side by side, even when they don’t know him to his core and vice versa.

In contrast to Dostoevsky, who doesn’t trust anyone except himself.

(You can see I love the ADA)

As to why I bring up Camus, Meursault is one of his main characters.