Although I don’t do full BluRay image backups, I know a lot of people that do, and seen quite a few posts about it on this forum. Go visit AVS Forum, and you’ll see there are more people with 50TB of storage than you might guess.
I don’t own a BluRay player, either, but I own around 400 BluRay discs. If I had more disc space, I would probably use full backups, because it’s much less work.
I’m not sure what you mean by “optiimized compression”…all modern BluRay discs use H.264 or VC-1 for their movies, and although it’s possible use a lower bitrate than most BluRay discs do, whether you see any visual difference depends a lot on what hardware you use to display, and exactly how you re-encode.
As for UHD BluRays, it’s still quite tricky to re-encode while maintaining correct HDR, so full backups are the safest way. You can save a little bit of space with a re-mux, but it’s not unusual for the main movie plus one audio track to take up 45GB, so you don’t really save much space.
If you want the best quality audio and video, BluRay is still the only way to get it. Also, there really isn’t any other way to actually buy an HD-quality video and have it available to you regardless of what kind of speed you have to the Internet.
But, based on some of your other posts, I see that paying for a movie probably isn’t something you do. I’m the first to admit that the movie studios are bloodsucking leeches out to drain as much money as possible from us, but as long as I can really own something and use it as I want (which is possible with BluRay), I’ll pay a reasonable price.