Yes, but «distorts the hue, lightness, and chroma relationships between colors as perceived by a large statistical sample of humans with typical color vision» (or perhaps easier, «... as computed using the CIE standard observer and a well-defined color appearance model») is not subjective.

You shouldn’t be “arguing” with the spec here or presuming to speak for “users” until you have studied up on color science, done concrete work with color reproduction, or at least compared both ways for yourself on a few dozen images.

Again, this is the naïve approach which is too often taken, but, contra your intuition, the results are dramatically worse if you do it that way. In an immediately obvious, not subtle way. What most “matters to the majority of users” is that their images look like what they expect. If you totally distort all the color relationships, the images end up looking completely different than intended, and “most users” will be dissatisfied with the output, blaming either the creator of the image or the software for being incompetent but without knowing quite what the problem is.

There are ways to avoid hard clipping, using a more sophisticated gamut mapping algorithm (I recommend you read Morovič’s book), but you can’t just treat one color space as if it were another.

In practice, hard clipping of out-of-gamut colors (assuming you do it along lines of constant hue/lightness in CIELAB space, or similar) ends up working reasonably well. You get some artifacts, but the vast majority of images stay away from the edges of the gamut.

(Photoshop and other Adobe apps have a pretty bad gamut clipping method, which is to map between color spaces without clipping, and then independently hard clip each color component. This sometimes causes severe hue shifts. Alas, even the industry leading software is often implemented by people who aren’t trained in color science, and don’t consider the edge cases. Or wrote their implementation 20 years ago and haven’t bothered to update it to keep up with computing improvements. It’s still much better than just pretending one color space is another though. I’m not sure precisely what Apple’s color management stack does.)

Most people care whether the colours look good to them, not how close it is to some standard they probably don't know about. Almost everyone buying monitors in a store are going to be strongly basing their decisions on the brightness and vividness of the colours.

What most “matters to the majority of users” is that their images look like what they expect.

...and that is subjective.

Regardless, if 241,0,0 looks identical to 255,0,0 on a monitor with 24-bit colour, that's just not right at all.

I feel a bit like a broken record here. There are ways of mapping one color space down to a smaller one without hard clipping to the gamut boundary. But these can be computationally expensive and difficult to design properly.

However, assuming that a better gamut mapping method is unavailable, hard clipping out of gamut colors in practice works much better than just pretending two color spaces are the same. When you do the latter, images end up looking terrible.

The effect is immediately obvious to anyone with standard color vision, and as such is no more “subjective” than anything when we’re dealing with perception. In some sense all perception is subjective if you want to get philosophical. But in a practical sense, not really.

If you have a copy of Photoshop, you can try this for yourself. Collect a number of photographs or other images encoded in a large color space like P3. Then convert these to sRGB in two ways, (a) using the “assign profile” menu option and (b) using the “convert to profile” menu option.

Your proposal is to do the former. In practice, the results are entirely unacceptable. They look bad. That is, if you collect a group of humans with typical color vision and present both options, they will pick option (b) for almost all images, and for most images the right choice will be very obvious to everyone.

Say there is a background colour in sRGB and an image in P3, and both should display the same colour visually. Changing the visual display of the P3 image just because it could include non-sRGB colours will make them not match.