I'd like to point out something awesome Eliezer did in the previous chapter, "Cheating". In canon, Potions as a discipline is hardly taught at all. The only thing you ever see Snape do in the books is give a list of ingredients and instructions, tell the class how long the class period is, and assign papers at the end of the class. This is one example of how J.K. Rowling wasn't really invested in developing the mythology of the universe, except as strictly necessary to make her plots happen. (There's nothing wrong with that; they're children's books, not "real" fantasy for adults.)

With the "Cheating" chapter, rather than trying to create a whole framework of Potions rules to understand as he's done elsewhere, he simply added a darn good explanation that legitimizes everything Rowling already showed us. When Hermione lectures Harry on "understanding the principles" in Half-Blood Prince, instead of scoffing about how there's never been evidence of any principles to learn, we can now imagine that there's a very good reason why Harry is never taught the principles of potion-making: if you're not smart, thoughtful, and careful enough to figure them out for yourself, you have absolutely no business knowing them at all.

When compared side-by-side as if they're in the same genre and directed toward the same audience, Methods of Rationality often makes the books look worse than they used to look. But in this case, future readings of the books will be made a little bit better. I wonder whether there are other ways that's true that I haven't noticed yet.