Sam2: you’re right. All I’m trying to say is that he has the power to do so as a Rishon. He doesn’t need to worry about the opinion of the majority of Rishonim. We do.
Just my hapence: the fact that we don’t have any letters today doesn’t mean he didn’t write any. I don’t think he’s making this up. I mean a little later in the paragraph he quotes the Abarbanel and Mahara”m Alashkar, the former who heard about this chazarah and the latter who seems to have seen a letter from the Rambam to one of his talmidim. The mechaber also says he has this letter in ksav yad (I assume of the Rambam).
The fact that he was a “super rationalist” is exactly the point. The mechaber on page 5 quotes the Rambam himself and explains all his seforim are based on his own shikul hada’as and sevora because he had never been taught nistar. I understand that he was working with what was available to him: his massive intellect and his eyes. Once he was given tools that extended beyond the intellect and the eyes, he was chozer.
Also I made a mistake. The mechaber is not the Pri Megadim.