At least the Marvin Gaye track is not a good example of just the Atmos difference. It is a completely remastered version that sounds nothing like the original. It also is 3.5 dB louder, which naturally would make the listener think it sounds better.

Overall, I think the OP was on point. It seemed like the mixing engineers thought that the additional spatialization provided by Atmos gives them the license to crank up the volume of all the supporting instruments (e.g. congas). This indeed drowns out the main vocal and puts it on the listener to focus on it (which is of course now easier due to the spatial separation with the instruments).

Personally, I didn't feel it was particularly great. All the sound seemed to come from in front of me and sounded like the stereo effects occasionally used in music tracks. Perhaps it's due to the shape of my head and ears not matching their model, as suggested in some of the comments above.