He's quite prepared in a Hero's Journey sense, though. In Harry's own mind, he has lost his mentor. Thus, he is now free to be a mentor. And what better way to grow, as a Hero and über-rationalist, than to teach others to do what you do?

I hope it plays out like this, at least in part. The bits early in the book with Harry teaching Draco were fun.

Harry would say that he's already doing that with Draco—but in the same way that he usually holds back his near-mode instrumental-rationalist dark side, he's holding back the kind of insights that Draco would need to think the way Harry thinks; Harry is training Draco to be a scientist, but not an instrumental rationalist, and therefore, in the context of the story, not a Hero. (To put it another way: Draco will never two-box. He's a virtue-ethicist who is more concerned with "rationality" as just another virtue than with winning per se.)

Draco may have already had the instrumental rationality part; certainly he was on a higher level instrumentally than epistemically. He had already had tutors in influencing people, he didn't have an akrasia problem, and he grew up in a culture of "find out what you want and go get it". Also, did you mean "Draco will never one-box?"