I enjoyed your reply. It reads well, and we can see the passion. Besides it, another thing I find impressive is this forum. I can’t recall a nicer company that’s more interactive and considerate to their users. When you read nearly all the posts here, you see this a dozen times a day. So I will politely disagree when people conclude less, but anyway moving on.
It seemed to me that in the last few years, Plex focused on creating GPU hardware acceleration and getting external streams up and running.
Yes. As you noticed HDR, Dolby vision, and ATV4K have been a challenge for Plex to master. You say you can’t speculate as to why, but you do a pretty good when you commented how Streaming is a river of wealth. It would be odd for Plex to prioritize other things besides microtransactions, which I bet are almost working. Good honest income pays for more devs, but this is just me guessing.
But when you say Disney gets billions every year directly avoiding the middleman, I disagree. They have to pay their ISP a catastrophic amount of money for the total bytes transferred (AT&T), and they have to pay to use distributed data centers that are resilient to DDoS. Maybe those two examples aren’t what you mean by middlemen, but we can’t physically see their service without them.
Back to why HDR, Apple TV, and DoVi have been difficult. One answer is that Plex uses 3rd party software like ffmpeg, mpv, and OpenGL to do these tasks. If Apple looks at their ATV telemetry and sees Plex users don’t subscribe to ATV+ or sees we are still watching their partner’s shows on Plex, they have every incentive to encourage us to use the real ATV+ app. How would they do that? They might, for example, know that displaying 8bit colors (SDR) within Plex uses the Apple OpenGL-3.0 layer. So they might choose to not upgrade the tvOS OpenGL layer to version 3.1 that supports 10bit (HDR) colors.
Then what? People subscribe to ATV+ and Netflix while Plex coordinates with 3rd party devs who are not paid.
Maybe it’s nothing like this, but if you think they work on color banding but not DoVi, I guess that’s possible.
In closing, change is good. Hopefully the future will be good for you too, here or among the barbarians of MegaStReAm Media Server. 
