Re ceteris paribus, I address simliar criticism here: https://news.ycombinator.com/item?id=10064126. The key point is that the original post I was critiquing was already implicitly keeping all other factors fixed. And I only aimed to critique that post's reasoning, not the conclusions it made.

As for imperfect competition (which I'm also familiar with, I have a PhD in economics), I see you mentioned it above but I still don't know why. Even if not sellers were a monopoly or oligopoly, everything I said above would apply, at least in very broad terms. You could probably come up with some demand function such that increasing input costs of a monopolistic producer resulted in an increase in production, but I don't see why you would think that actually applied here.