What is HDR, anyway?

This! Yes I think you’re absolutely right. The term “HDR” is in part kind of an artifact of how digital image formats evolved, and it kind of only makes sense relative to a time when the most popular image formats and most common displays were not very sophisticated about colors.

That said, there is one important part that is often lost. One of the ideas behind HDR, sometimes, is to capture absolute values in physical units, rather than relative brightness. This is the distinguishing factor that film and paper and TVs don’t have. Some new displays are getting absolute brightness features, but historically most media display relative color values.

Absolute is also a funny size. From the perspective of human visual perception, an absolute brightness only matters if the entire viewing environment is also controlled to the same absolute values. Visual perception is highly contextual, and we are not only seeing the screen.

It's not fun being unable to watch dark scenes during the day or evening in a living room, nor is vaporizing your retinas if the ambient environment went dark in the meantime. People want good viewing experience in the available environment that is logically similar to what the content intended, but that is not always the same as reproducing the exact same photons as the directors's mastering monitor sent towards their their eyeballs at the time of production.

Yep, absolutely! ;)

This brings up a bunch of good points, and it tracks with what I was trying to say about conflating HDR processing with HDR display. But do keep in mind that even when you have absolute value images, that doesn’t imply anything about how you display them. You can experience large benefits with an HDR workflow, even when your output or display is low dynamic range. Assume that there will be some tone mapping process happening and that the way you map tones depends on the display medium and its capabilities, and on the context and environment of the display. Using the term “HDR” shouldn’t imply any mismatch or disconnect in the viewing environment. It only did so in the article because it wasn’t very careful about its terms and definitions.

Indeed. For a movie scene depicting the sky including the Sun, you probably wouldn't want your TV to achieve the same brightness as the Sun. You might want your TV to become significantly brighter than the rest of the scenes, to achieve an effect something like the Sun catching your eye.

Of course, the same thing goes for audio in movies. You probably want a gunshot or explosion to sound loud and even be slightly shocking, but you probably don't want it to be as loud as a real gunshot or explosion would be from the depicted distance.

The difference is that for 3+ decades the dynamic range of ubiquitous audio formats (like 16 bit PCM in audio CDs and DVDs) has provided far more dynamic range than is comfortably usable in normal listening environments. So we're very familiar with audio being mastered with a much smaller dynamic range than the medium supports.