Is there anything more “Physicsy” than a harmonic oscillator?
Feynman diagrams are all fine and good, but what percentage of physicists actually use then, or even learn about then? I do use then (in cond mat), and teach then, but in an optional course that only some theory students take. You can be a perfectly fine physicist without even knowing what a Feynman diagram is. You cannot be physicist and not know what is a harmonic oscillator/normal modes.