I'm sensing things here too, but it's not irony.
Ah, now we've changed the game. You're saying that the resulting downscaled image will have the same reduced colour depth as the original image. This is not what you have been saying up until this point.
You said that "4K has 4 times the color depth (and 4 times the bit rate) of full HD" which implies that I can film a 4K 8-bit image and get greater colour depth than FHD 8-bit, but now you're saying that the resulting downscale to FHD will have the same limitations to colour depth, which completely disagrees with your original statement.
Correct.
Which is why "4K has 4 times the color depth (and 4 times the bit rate) of full HD" is a fundamentally incorrect statement.
I shoot with 8-bit, I get colour banding.
I shoot with 10-bit, I don't get colour banding.
Seems like it has everything to do with the colour depth of the resulting image.
Please provide links to any articles or definitions (or anything at all) that talks about how colour depth is different to bit depth, because I have looked and I can't find a single reference where someone has made the distinction except you, who it seems suspiciously like you're changing the definition just to avoid being called out for posting BS online.
Then explain it simply.
I have asked you lots of times to do so.
The really sad thing is that there is some basis to this (and thus why Andrew and others have reported on it) and there are some situations where downscaling does in fact have a similar effect to having shot in an increased bit-depth, but you are not explaining how to tell when these situations are and when they are not likely.
Making assertions that resolution can increase bit-depth but then saying that banding will still occur is simply disagreeing with yourself.
For those having to read this, firstly, I'm sorry that discussions like this happen and that it is so difficult to call someone out on them posting BS misleading generic statements. The reason I do this is because as I've learned more about film-making and the tech behind it, the more I've realised that so many of the things people say on forums like these is just factually incorrect. This would be fine, and I'm not someone who is fact-checking 4chan or anything, but people make decisions and spend their limited funds on the basis of BS like this, so I feel that we should do our best to call it out when we see it, so that people are better off, rather than worse off after reading these things.