But it does reflect the underlying theory (though it does take special cases and simplifies), and it does present a pedagogical simplification (because it's a hell of a lot easier than solving huge quantum systems. Heck, it's not even a metaphor. A DAG is blank enough - has few enough intrinsic properties - to be an incomplete model instead of a metaphor.

Does anything other than a fully quantum description of a system using only an interacting-particle hamiltonian with no externally applied fields count as a non-vague non-metaphor?