The analysis is fascinating but the conclusion (including the title) doesn't seem to follow. It would be a mistake to attribute a significant amount of the success to poor calculations by a few fanfic commentators when more standard explanations are possible.

They put a major marketing campaign behind it. And since 40% of readers will finish anything, absolutely anything, that they have started reading, they sold millions of copies. Just as they would have with almost any book they'd marketed as heavily.

You don't create the fastest selling book of all time by picking a random manuscript and advertising heavily. It "Just" isn't possible to achieve such extreme results with 'almost any book'.

Moreover, the most important part of marketing is understanding what product the market will be easily persuaded that it wants. In this case they chose a story that takes a particular kind of wish fulfillment power fantasy had by a huge audience and expresses it in a pure and blatant form. This is not something that the publishers were not familiar with.