One more hypothesis after reading other comments:

HPMoR is a new genre where every major character either has no character flaws or is capable of rapid growth. In other words, the diametric opposite of Hamlet, Anna Karenina, or The Corrections. Rather than "rationalist fiction", a better term would be "paragon fiction". Characters have rich and conflicting motives so life isn't a walk in the park despite their strengths. Still everyone acts completely unrealistically relative to life-as-we-know-it by never doing something dumb or against their interests. Virtues aren't merely labels and obstacles don't automatically dissolve, so readers could learn to emulate these paragons through observation.

This actually does seem at odds with the western canon, and off-hand I can't think of anything else that might be described in this way. Perhaps something like Hikaru No Go? Though I haven't read them, maybe Walter Jon Williams' Aristoi or Ian Banks' Culture series?