Just the span of wavelengths isn't the only thing that's important, the spectral resolution is also important. For example, theoretically with 6 different cones we would be able to tell the difference between the mixture of red and green wavelengths vs only seeing yellow wavelengths.

Or the mixture of blue and red wavelengths vs violet wavelengths, which just happen to be at the furthest possible point from the red wavelengths. Human color perception is strange.