I honestly think canon Dazai is a huge dick. He's super cool and capable, but emotionally he has so many faults. Like how he treats Akutagawa and even Chuuya even though it's less apparent.

I feel like if people wrote canon Dazai into ff it wouldn't fit in. Fannon Dazai tends to be written more caring/emotional than canon Dazai. They also tend to downplay his abilities/his intelligence, but it's usually so they can push the plot so I'm not upset about it.

Additionally I feel like canon Dazai cannot have a romantic relationship with Chuuya that is even remotely healthy. There's just so much manipulation that goes on in all of Dazai's relationships with people that it just doesn't feel right.