Hmm I do not believe the story itself was retconned, but maybe the author really did rush it a bit due to backlash. The NTR baiting is weird but Japanese always have a very heavy handed approach to this, and NTR baiting is not only often considered a good marketing move but cucks are amazing paypigs who must make up a large share of manga readers (also women). Though for the story itself, I bet my paycheck that majority of paying readers would be older men who absolutely detest cuck shit. I think the author just fumbled immensely. Hopefully because the story focuses a lot on Washio's mental health issues and mental health issues and cuckold goes hand in hand (and the story is sourced from the author's mind, which must be sourced from author's own experience, at least in some capacity).
I think it was meant to be this way, but maybe some details changed (like the nature of relationship between the dragon and the scientist and I think everyone will agree its a good thing). The sudden 180 in Washio's behaviour is not out of character but very much in character. Back then he did what he thought is right, not what he truly wanted. All he needed was just some proper guidance or a catalyst to wake him up. People like Washio dont care about their own misery or they even feel that they deserve it. But when someone close to them is in danger the part of them that is in opossition to their self destruction can finally act and safely (for the ego) project itself onto someone else ("I am doing it for them, not me", notice how this is the same motivation that made him reject spider and leave in the first place). This is why usually passive dejected Washio suddenly bolted and rose into action like it was natural to him. I am pretty certain that this is what the author was aiming for, but as you can see its a very complex jumble of emotions. Thus the fumble.
Tl;dr salaryman's feelings are complex