Yeah, but there is precedent for audio blu-rays shipping with Atmos and non-Atmos surround mixes, e.g. Abbey Road.
And some people are claiming the mix is unimpressive on their systems, some of whom do not have Atmos capability.
I'd be pissed if I were them and there were no chance to try a dedicated 5.1 mix.
Actually, Mike, most UHD4K discs only have an ATMOS/7.1 option but fold down successfully to 5.1 with NO PROBLEMA!
Getting a headache.
For everyone at home with only 5.1, try what I just did before going nuts about it.
Put in your Abbey Road and play it in Dolby Atmos.
I can hear everything I hear in the DTS-MA 5.1.
When I listen to Octopus, the bubble noises Baggins extracted from the height speakers in his YT vid are in the sound field quite nicely, thank you.
[Sony X800 HDMI into Yamaha 5.1 AVR]
At ease.