Keep in mind, Methods of Rationality is an alternate universe story.
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The one big point of departure is a bunch of prophecies back in the time of Merlin. This causes Merlin to create The Interdict of Merlin, with the goal of reducing the power level of magic down to where it is no longer a threat to existence. This is necessary to give Slitherin's monster a much better reason for existing. In the original books, it was just something to threaten muggle-borns with. Now, it became a way for Salazar Slitherin to pass knowledge down to someone in the future, and bypass the Interdict.
It is the prophecies, and Dumbledore's listening to them, that leads to Harry's pet rock being destroyed/killed, as well as everything else.
It is the crazy behavior of Dumbledore, against the logically sane behavior of Quirrel, that leads Harry into being the person that he needs to become.
People complain that there are more time turners here than in canon. The truth is, we have no clue how common time turners are in canon. All we know is that Hermione had one in canon, and there are two (maybe three?) known in this story.