ISO, & the use thereof

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Which device were you referring to when you mentioned video settings in your post?

In those terms, ISO priority = dynamic range priority. Useful in landscape photography.

What if you were shooting at 240fps; would you need 1/500? Unless I was going to want to rip out individual frames as stills that need a fast shutter speed, I'd use 1/320.

I used to think that you could get away with faster shutter speeds at higher frame rates, but after buying a 360fps laptop, I've found that you need blur for motion, even at that framerate. Any sharp edge that moves more than a couple of mm on the monitor between frames will appear as a multiple exposure. So, while 180 degrees seems to be a good compromise between stuttering and too much blur at 24fps or 30 or 60fps, that shutter angle is not going to be near-optimal over the entire range of potential framerates. For very low framerates, you are going to have a "fast slideshow" type of effect, anyway, so fluid motion is less expressable, and you may as well look at sharper "slides", and at the very fast framerates, there may be no utility in truncating exposure time at all, and rows of pixels should probably be reset immediately after they are read if the video is to be used as video, and not as a burst of intended stills packaged in a video file.

So let's say you had a 600fps video camera; you'd probably want to use ~1/600.01 exposure time, so that motion is as blurred as possible, and also, you'd have almost zero blackout at any pixel (just the read/reset interval), so you could resample the video temporally, without any temporal aliasing artifacts, or individual ghosted (multiple-exposure) frames in a slower-fps output.

I have no idea what you're trying to say there. "ISO priority" literally means that ISO is the only thing you want to directly control, and that you'd like to let the camera choose f-number and exposure time.

Then I didn't fully get the idea of that proposed 'I' mode (I didn't mean 'P' with manual ISO was good for landscape photography).
When you set ISO first, it can be called 'ISO priority'. In camera manuals, 'priority' is just the setting you control manually. So P, M, Av or Tv with manual ISO all can be called 'ISO priority'. It doesn't need to be the 'only' thing you control. Say in Av you may control both aperture and ISO.

Canon invented this new Fv mode ('Flexible') where you can switch between 'priorities', that is, you can switch between the settings you want to control manually. The mode came out quite clumsy in my opinion, but you can actually control whatever you like, e.g. ISO, and the camera will set f-stop and shutter speed automatically. And then you can tweak f-stop manually.

You'd do well to take ownership of what you write and simply acknowledge a mistake rather than attacking someone for bringing it to your attention.

If you called a mode "ISO priority", then it clearly and definitely says that ISO is "more fixed" than either the exposure time or the f-number.

How can it be 'more fixed' if I manually control, say, both aperture and ISO? If I set them independently, they're both the same 'priority'. Or I'd argue if I set ISO first and then aperture, then it's 'ISO priority'. In which case the priority is chosen manually. Higher priority is just whatever I set earlier. It's the case in ETTR where I typically set ISO first (to 100 or sometimes 400).

That is your opinion to have and that's fine.

People are forming their own opinions on your honesty and integrity based on what you and I wrote and that is the way it should be 😊

I posted I lock in base iso only when using a tripod and there is no movement in the scene.

I added that auto iso sets base iso when appropriate.

In both cases the base iso shots are usable.