So this is not a misunderstanding, but the real reason why magenta (red+blue) is perceived similar to violet (shorter wavelength than blue) by human eye.
What you’re finding is the CIE “color matching functions”, which is closely related but not the same thing as the raw physical response of the cones. Here is a paper describing the difference, and more current research than what you found: https://hal.archives-ouvertes.fr/hal-01565649/document
Look specifically at page 2, and the linear relationship between the color matching functions (where red has a left-bump), and the “fundamental sensitivity” plot, which is attempting to find raw physiological cone response to different wavelengths, rather than what the observer perceives.
https://www.researchgate.net/figure/Normalized-spectral-sens...
So this is not a misunderstanding, but the real reason why magenta (red+blue) is perceived similar to violet (shorter wavelength than blue) by human eye.