I'm going to put myself in the firing line and actually defend Gazing.
What he is really challenging is this assumption
7) Regardless of how many workers I put on making DLC, it will result in 15k/month.
or as Gazing put it: "You have shown no [or zero] causation between the number of employees and the expected revenue."
From the System engineering side that Gazing is talking about, you have a resource that produces widgets at a rate. Which in this case is a developer making DLC pack content per month. Using 2 resources in theory results in 2x the production rate of widgets a month, so 2x as many DLC or a single DLC worth 2x the content. So twice the income a month?
However, as Gazing admits it's not that simple:
"I know that such a causation exists, and that it is quite difficult to calculate or predict"
That's because 2 workers/resources don't always produce twice as much, and twice as many DLC or a DLC of twice the content, might not sell for twice as much. This is 1 of 2 really tough parts of the problem, Brad has to predict how his rate of return per developer scales with more developers to a DLC. He may already have predicted it as not scaling at all, which is a harsh thing to tell us but may be true. (We will always be willing to pay 15k/month for the DLC regardless of how much or little content it contains). As Brad already mentioned the 2nd really tough part is that he has to predict the same rate or return per developer on other projects, and compare the two options, or opportunity cost.
Which brings a question to ask ourselves: Would you buy x value of DLC a month regardless of how much content is in it? Would you buy 2 DLC packs a month comfortable that they took 2x the effort combined or buy one dlc for twice the profit? How accurately do you weight the contents of a DLC before buying? I'd love to say I'd shell out more money for more content, but deep down, I don't think my estimate of value is accurately scaled to the effort of content that went into it. Also, the forum going crowd is going to be the more interested customers, so if we all say we'd subscribe to 15$ a month, Brad still couldn't easily extrapolate that out to his general customer base.