With regard to DD Atmos
versus BD Atmos....
The bitrates for streaming have recently increased thankfully. I have a modest, Big Box Store type home theater setup. Not audiophile, but also not terrible. Full Atmos 11.2 system. Nice Polk bookshelf’s and two 12” 600w subs. I did not find the difference in audio between Atmos on disc versus Atmos on streaming wildly different. In fact what was more damning was losing Dolby Visions superior image over BDs HDR10. Even on streaming (ATV) DV looks superb. Per scene color balancing makes a huge difference. Color, vibrancy, range of image IS something I find quite noticeable.
I have quite a few 4K BDs that are mastered in Dolby Vision and with the tone mapping on the 77C9 the HDR ones look pretty good too.
Yes discs are 'old skool' but with the disc I always get what I expect for audio and video. With streaming I still get a softer picture with less detail and less color saturation than I get with a disc. Additionally if the bit-rate being delivered for the stream is not rock solid there will still be occasional dips in picture quality evidenced by posterization, pixelation or even a change in resolution in rare cases.
4K on disc offers absolutely the best "theater quality" experience possible in the home. Streaming though is more convenient.