Prime 4K's bit-rate is ~15Mb/s. A UHD Blu-Ray has a bit-rate that's more like 70Mb/s, and a 1080p Blu-ray has a bit-rate of ~28Mb/s. Of course, 4K is usually encoded with H.265 while 1080p is encoded with H.264, so the raw bit-rate numbers are not as useful for comparison - but still, that's almost twice the bit-rate for a quarter of the pixels, and H.265 isn't magic.
If you have a fancy 4K TV and a decent sound system with Atmos which you want to take advantage of then you really should be buying physical media instead of streaming... I mean, if you went beyond having a sound bar, and ran wires for surround speakers with a proper home theater amplifier.
Streaming platform usually only give you 5.1 on EAC3 (DD+), on UHD Blu-rays you get 7.1 over TrueHD, and then you get Atmos on top of both of those, and Atmos over TrueHD is more Atmosy or something (besides obviously TrueHD being lossless while EAC3 is lossy.)
Here in Mexico at least, there's almost no 4k content on Prime. Even less Atmos content.
Netflix, Disney, and Apple are great.
HboMax has 4k content, but their tech is really bad and the quality is constantly jumping between SD to 720p to 1080p to 4k. We have a 500Mbps fiber connection.
