Heyhey, nice overview, though on the "just works" thing on atomic/immutable distros I want to say that that's not the case by virtue of a system being atomic.
I'm on Fedora Atomic (which Bazzite layers on) and the codecs you'd expect being on there aren't because of licensing (just like all of Fedora's distros).
I also don't believe Fedora Atomic does anything in particular in regards to drivers. So the advantages you're talking about are there because of the people who worked on Bazzite.

On breakage, it's definitely not a bad thing for a system to *gently* push users into installing software in user space and with some isolation, but it's far from a requirement for a stable system.

And if you're going to be layering everything anyway (so installing basically only installing using rpm-ostree), you're not gaining much by choosing an atomic distribution. Those layers can conflict like with any other distro packages

Fedora KDE, which I ran for almost a year, has not given me any issues except for the codecs which I had to install myself.
It's actually more of a pain to get codecs to work on Fedora Atomic because of how RPM Fusion needs to work with layering (https://rpmfusion.org/Howto/OSTree), which wasn't an issue on standard Fedora.
So you'll end up needing to manually updating the repository RPM Fusion repository every 6 months.

Also some software, like Steam, is also a pain to work with when using the Flatpak. \

VanillaOS (which *doesn't* use rpm-ostree since it's based on Debian) and Bazzite are both good atomic distros if you really want that, while having those kind of annoyances handled for you.