> I think the explanation is simple: Color is light and it is linear going from ultraviolet to blue to green to yellow to red to infrared. It's just a line.
The most common misunderstanding of color is that it has any property extrinsic to the seer. Color is in the mind.
> In physical reality, there exists no purple light.
In what you imply is physical reality (optics) there's no color at all.
> Our minds make up all the shades of purple and magenta between blue and red when our eyes receive both red and blue light.
To repeat, your mind makes up every color. It's a category error to imbue light with a trait of color independent of the seer. In color science, what you refer to as physical reality is more precisely termed spectral power distribution of electromagnetic radiation in the visible range.
To the extent that radiation stimulates a color response for the human visual system, there most certainly is purple light, it's just not simulated by a single narrow band of radiation.
As you have attempted to note, The CIE horseshoe diagram (spectrum locus) illustrates this with the "purple boundary" at the bottom, which represents the perceptual edge of mixing long and short wavelength stimulus (red/blue primaries).
But to presume that there's a natural color of light is a distinctly human biased statement of reality. Different creatures have characteristic responses, with very different traits from humans. Imagine having sensitivity to polarization.
The artist's color wheel is circular because that's how color as qualia manifests in the mind of the artist. The physics of the qualia are more with complex intrinsic response of the organism than the extrinsic stimulus.
To speak of the color of light is common sense, but over-imbues the physics of the stimulus with human traits.
Make explanations as simple as possible but no simpler.
> ...Meaning you have to bend the real color line. And that's what we see in the chromaticity diagram.
Any explanation that regards "real color" as a trait of light rather than of perception misleads more than it clarifies.