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.