That's mildly incorrect. As an author Dazai was multifaceted. He was, at core, a lonely scared child who was incapable of growing into a functional man. On the surface was playboyism, literary elitism, pretense, alcoholism and drug addiction, and a cool urbanity, all of which were merely acts to hide himself from others.
In the LN Odasaku comments that Dazai is "a child too smart for his own good" and that he gets into depressive fits because of it. In one of his short stories Dazai is writing about himself from a third person point of view (he's a background character in it, Das Gemeine) and it's said of him, "the expression of a child in anguish momentarily crossed Dazai's face". Those are VERY similar. The author of BSD certainly is familiar with the historic Dazai. The nature of the character is just rather subtle.