Since the mastery approach paid such close attention to readiness, prerequisites were better thought out. The prerequisites for literature at a certain level were not merely lower levels of literature. They also included the study of history, languages (Latin first, then Greek), rhetoric, and so on.
There's no single, objectively correct sequence, even for STEM subjects. But a master teacher can learn from experience what should be learned first, and to what level, to make a student fully ready to learn any given thing. Then take many experienced masters, put them together, and have them carefully work out a prerequisite tree from which they derive a sequence of instruction.