would Jouno scarejumping everyone in a Light Snow car bolster the point? that noone remembers gun children would kind of mean the fluff action is performed properly - enjoyable in the moment only to be forgotten as a mostly irrelevant point.
to salvage the setup: real selective killing would be in the past, and enough fuckups/pressure would have him be progressively more extremist about it. People do make reads on how BSD is absurdist at it's core - which would mean no plans perfectly coming together*. Plus, while he appears to be opportunistic about how genocide is carried out (DA, DoA), the primary plan seems to be the Book - and anyone with the book can retcon everything they did in the past. That said - and wouldn't it be funny if neither of us read Dazai's Entrance Exam - part of it is probably to signal Dostoy is way WAY further gone than that particular obstacle.
the post seems like noticing a novel Franchise Original Sin: sometimes it's character driven drama and sometimes it's just cool shit with abilities, and the bits of Meursault you dislike are an extension of the latter? Death Note jungle gym & dumb nonsense chatter to lower tension for Action Flick Shit elsewhere, if i remember properly?
*would all of this be a problem if Dazai fucked up badly in the main manga? earlier, hopefully?
At what point does a character become so evil that they're just irredeemable? Because I can ignore the Meursault arc by setting my story before it, remove Fyodor from some of the more catastrophic decisions made by the DOA and Guild, which at least bring him back down to some sort of relatability but... how can you redeem a man who manipulated a little girl into blowing herself up? Who put guns in the hands of children? It's so... evil. I can write Fyodor as a previously mostly good person, who took a horribly dark spiral into a delusional genocide mission. It's hard, but I can, so long as he doesn't succeed very far. Even killing Karma, while still an evil action, is questionable, debatable, to the reader. Because you can understand why Fyodor did it: he saw ending Karma's life as the only way to save him from a lifetime of torment and sin. And the reader can question how much they agree with that decision. And that's fine; I like that. But the little girl? It's the same principle, in theory: Fyodor could justify it to himself by saying that he wanted to save her from the sin surrounding her, to send her to God before she had the chance to sin. But that's where it breaks down. Because it becomes such a flimsy excuse, trying to mask such a massive evil.
Maybe I'd take out the kids with guns. That's too much, unless I'm missing something. Have the long walk through the tunnels with Atsushi and Kunikida be tense instead, them peering around every corner, ready for a harrowing fight. Kunikida's gun held tight, Atsushi tensed and ready to tiger out. Both peering through the darkness, only to reach a clearing in which stood a tiny little girl, hands clutched in front of her, scared, with some strange kind of necklace. And then in the next horrifying moment they realise: it's not a necklace, but grenades. Then the scene plays out from there. Not only would this be more impactful as a scene (in my opinion), it'd also characterise Fyodor in a different, much more interesting and nuanced way (in my opinion).
Because in that situation, it's only the little girl he's justifying to himself. And it's a bad justification, clearly paper-thin, but he believes it. And that makes the underlying horror and twist of Fyodor's character all the better--now that you've trimmed the fluff, that one point speaks so much more. You've emphasised that Fyodor's the type of person who's willing to manipulate a little girl into blowing herself up, but you've also shown that he put deliberate thought and care into that decision. It was to break Kunikida, but it was also to save her, to end her life before she fell into sin. And you would remember, because of how impactful the scene would be (whereas I'd bet a lot of people don't even remember Fyodor had gun children).
I think that's a problem the entirety of BSD (or maybe just manga in general) has. There's too much fluff action. It waters down the truly impactful scenes and breaks down the interest in characters like Fyodor. Because when he's killing very selectively, not only can you show how he rationalises those deaths for the sake of his plans and have that not be broken by continuity, but you get so much more out of those deaths. And if nothing else changed, and Fyodor was the only antagonist who didn't kill wantonly, imagine how different that would make him feel. His plans by their very nature would be new, interesting, contrasting. An antagonist who uses precise and measured deaths, just a pinpoint here, to achieve a much bigger effect on the characters than even the destruction of Yokohama by the Guild, would be something both new and far more terrifying.
And it would show how well Fyodor understood the ADA, that with just one death he could shake them so much--and how little they knew him in return would be very worrying. Imagine how much better his conversations with Dazai--the discussion of saving people would have so much meaning if Fyodor wasn't a hypocrite who killed people for no reason. If Dazai says that people are worth saving, and Fyodor agrees, even though they've entirely different meanings behind those words, and the meaning is actually there- imagine the subtext, the intrigue, the actual good writing that could come of that. God, I really wish it was so.