Banding is a symptom of insufficient color depth, and that's connected with HDR. More dynamic range requires more levels of brightness, specifically, 10 bit color depth for current HDR. Wide color gamut lets the TV display higher saturation colors. Although HDR TVs tend to have wider color gamut, there isn't any technical connection between HDR and WCG, and WCG doesn't require a higher band width signal.
Sadly that is in fact
totally wrong. There is more than sufficient colours inside an 8bit colour space. If what you said was true, then every single photograph that you take with a digital camera would come out with blazing banding and there would be riots in the streets because instgram would have failed. Oh the HORROR.
The banding you see it due to terrible artifacts caused by excessive compression. if you look up how H.264 works, it takes this massive amount of data and tries to compress it in a manner that has the least amount of visual impact. Sadly if fails quite badly at it. One of the techniques to compress an image is like a .jpeg where it cubes off a section of the image and then describes the colour of each pixel block by an offset to it's neighbouring pixel block. But even that takes up quite a bit of data space. So rather than doing each and every pixel, it starts to group almost near colours as just being the same colour. When you reach a point that the difference exceeds the delta, then you step up to another colour group. But sadly where you might have had 20 different colours, it has grouped all those as being a single colour. Then the next group can be a good 20+ shades of that colour different, so you get a band.
To see this in action. Take a photograph with a camera. Load it into you computer and then successively save it as a new jpeg with a higher and higher compression ratio. As around 80% compression you will start to see it slightly, but get to around the 40-45% compression then you will see a definite banding effect on just about any shadow surface where the colour gradually change to darker.
You must remember that the H.265 (the newer one for UHD) they are looking compress the video stream to 1/600 to 1/1000 of it's original size according to the spec.
