As a FreeBSD user that has had root zfs for a while, and used zfs on solaris before that doing the same thing. Explain how it isn't worth it?
Made backing out of patches easy mode, snapshot, patch, reboot, if its effed up, go back to the snapshot with a reboot. The only thing I've seen that comes close is NixOS, but it takes a completely different take on those kinda things. Better in some ways. But zfs root is great, means you can just set compression on for log dirs and don't need to worry about compressing logs. Fs takes care of that for ya, now grep works fine, no zgrep etc... needed.
I honestly can't see why you wouldn't want to boot off it. Hell I just upgraded my FreeBSD nas box at home, took a snapshot of the entire pool before I did just in case things went south. It may not be as performant as some filesystems, but to be honest, with nvme ssd's, its a non issue.
So explain how it isn't worth it in your opinion? Experience for myself has proven otherwise. And made me loathe BTRFS for being so behind zfs of even 10 years ago. (I've had BTFS zero out data for a Makefile I had open while running make, if it wasn't in a git repo I would have been super pissed off)