Do they? Do people report that an HDR image on a web page that takes up roughly 10% of the screen looks more realistic? Do they report that an HDR YouTube video, which mostly consists of a screen recording with the recorded SDR FFF being mapped to the brightness of the sun, looks pretty? Do people like when their light-mode GUI suddenly turns grey as a part of it becomes 10x the brightness of what used to be white? (see e.g https://floss.social/@mort/115147174361502259)
Because that's what HDR web content is.
HDR movies playing on a livingroom TV? Sure, nothing against that. I mean it's stupid that it tries to achieve some kind of absolute brightness, but in principle, some form of "brighter than SDR FFF" could make sense there. But for web content, surrounded by an SDR GUI?
> when their light-mode GUI suddenly turns grey as a part of it becomes 10x the brightness of what used to be white
I don't know why you're asking me about examples that violate the rules I proposed. No I don't want that.
And obviously boosting the brightness of a screen capture is bad. It would look bad in SDR too. I don't know why you're even bringing it up. I am aware that HDR can be done wrong...
But for HDR videos where the HDR actually makes sense, yeah it's fine for highlights in the video to be a little brighter than the GUI around them, or for tiny little blips to be significantly brighter. Not enough to make it look gray like the misbehavior you linked.