All of these are “root” mounts. I don’t explicitly mount any subvolumes (they get “implicitly” mounted as folders though)

Just let some bees loose on your system for a while and they’ll sort that out.
Also depending on how good your CPU is btrfs compression would also save a fair bit. AFAIK shared libraries are pretty well compressible.

I wonder how well it integrates with hardware. Arch with the pacman packages has been the only distro where I could get ROCm working reliably. I’d love to make a “ROCm container” and dump all that mess into it’s own sandbox.

In fact, the thing I really want is more of a “Qubes but not for security tryhards” (aka I can actually use Wayland AND game on it) where everything gets it’s own container mainly for organizational purposes, but something like this sounds like a fair compromise.