The point is that yellow is its own thing. The psychological yellow is neither red nor green. If you don't understand the analogy, then my advice is just move on and don't get hung up on it.Adding different shades of yellow of course makes it more complicated. Still, a certain small part of the visible spectrum is yellow. Why else would you use it as a spectrum analogy?
Cones are a reason why the analogy fits better to a combination of primary colors. You can absolutely reduce yellow perception to a combination of M and L cone responses as you point out, and yellow is not a separate thing then. Maybe I misunderstood your analogy, cause from my POV, you're arguing against it![]()