I agree for the most part. I've found once I got my TV settings just right and HDMI settings just right, there was no need for me to switch between SDR and HDR, that I could just leave it on the best possible settings that the Apple TV offers and everything looked fairly exceptional.
This really depends on your TV and what it's capable of. I'm glad you found settings that equalize it for you. However, while my Sony 900E has very good backlighting, HDR, tends to be a bit dimmer, which is fine when watching a movie in HDR in a dim room. However, it's terrible for daytime viewing of anything. Whether Apple intends to improve their SDR over HDR implementation, or not (and we all know of what the road to hell is paved), they can't possibly take this into account for every TV on the market. And many TVs are just not going to have the nits to run HDR full throttle in every circumstance. That's why at a minimum, Apple needs to offer native output as an option.
For streaming content like Netflix and iTunes, is there a way to tell what format the source material is in? In most cases the info just shows HD or 4K (sometimes HDR) but no refresh rate. If HDR is not indicated I'm assuming the material is SDR and would be best viewed in SDR rather than HDR setting. Is that right?
On iTunes no, there's precious little information. About the best you can do is swipe up and see the format you're receiving for that device. Netflix was giving a bit more information on my Android app, but not sure about the ATV app. If it doesn't say HDR or DV, then yes it's likely SDR. If it's a movie, then 24Hz is likely the best setting, as 24fps is the standard for films. TV is likely 30Hz, though some, especially those Netflix shows that shoot in Univisium, may also use a film frame rate. A lot of it will depend on your TV whether you need to be concerned about the frame rate. A 24fps film will look most natural at the native frame rate. At 30, or 60, some pulldown will be interjected that can make the film look off, particularly in panning shots. That's where your TV comes in. How effective it is at smoothing out the picture without producing a soap opera effect, will determine whether you can leave at at 60Hz for everything, or prefer switching it to 24Hz. So far, I have not been impressed by the ATV 4K upscaling capabilities, nor it's motion handling capabilities, compared to my TV. So, I've been switching to the proper native format (in some cases guessing), and let my TV do the work it was designed to do. In most cases, I personally think it looks better. In other cases, it's hard to know whether I've guessed at the native frame rate incorrectly, or the ATV is doing a better job.
Unfortunately Apple has not given us the choice, and seems intentionally preventing us from getting native formatting information to make manual adjustments. But in the end, its going to depend on what looks good to you, with the equipment you have.