I was able to solve all my issues:
1. I disabled all the motion smoothing and set it to custom with judder reduction to 0 basically. The effect I was referring to that made things look terrible is referred to as "Soap Opera Effect". It is unreal how terrible it is. Google it. But I think I mostly got rid of it.
2. I set the colour space to auto instead of native (yeah seems like native would be better right?). When it was on native, it would always be stuck on RGB, switching to auto, I now get Y′CBCR 4:2:2. Highly recommend
3. Upgraded firmware and have not seen the Dolby Vision HDR problem since.
4.
Shield has a menu item for frame syncing. Highly recommend. The sad part is, I need to press it every time, but then I get native frame rate. (ie. 24fps instead of 59...hz on Dolby Vision)
5. Using ARC to talk to my amplifier which is quite old (Onkyo TX-SR313), but haven't run into any problem using that mechanism.
General note I would say is: Keep checking the info in support menu to see what the screen resolution and color space is set to.
I already configured my Shield to use native colour spaces, etc. that probably is required for colour spaces other than RGB.
I am progressively more inclined to upgrade to the new shield and when I do this tip will save me hours of fiddling. Unfortunately the shipping from Amazon has become pretty expensive since the lockdown, so I am holding on a bit.
Check the Nvidia Shield thread. I posted a pick there, you can pick it up for R5k now. That said, if you have the previous model, the reviews show it is not worth upgrading. You may want to consider only getting the new remote. I haven't once used the IA upscaling and that is the big "sell" on the new version
3. THIS! I too have the Nvidia Shield and this problem is annoying me endlessly. I am using the IR on the shield remote to power down the TV but CEC power off would be sooo much better.
Ended up doing the same. The Shield TV Pro remote is the best remote I've ever used. Definitely not going to be using the HiSense remote.