That it's louder than the rest of the program. You pointed to the levels of the left and right, but they're not a single instrument, they're multiple instruments combined so of course they should have a louder level than just the guitar solo. I use the Marantz app on the fly to quickly adjust channels, for example at night once the kids are sleeping I'll put the subs to -12dB and the centre to +4dB. Usually they're at 0dB for regular listening. Leash sounds better to me with the centre at -2.5dB in Atmos, but I wouldn't walk out during playback without it. Typically if I'm going to mixdown to stereo to get a better sounding album (from a dynamic range standpoint) than what we got from the approved stereo mix, I don't have to make individual channel adjustments for volume. The new Slowdive record mixed from Atmos to 2.0 sounds so good. Try doing that with Leash and see what happens at the guitar solo, it's...jarring.
I'm glad you enjoy the levels, but it's neither here nor there for me because I'll likely only listen to the tracks I've listed. Leash, like much of Pearl Jam's Atmos output, just sounds muffled to me and narrow. I'm sure you must notice a huge difference if you switch from Leash one minute in to W.M.A.? And I don't just mean because it's a little louder - it's actually a really good mix, one I would pay for. It's not surprising to hear two different people worked on the mix, and it's pretty clear they were not working together because then the mix would be coherent.