ZFS was never going to have good support for adding and removing drives of arbitrary size. It's a filesystem for people who buy their drives by the dozen.
It works completely fine with a single drive - just as well as any other filesystem, if not better. As a single root/boot drive’s fs, it’s far batter than any of the “standard” alternatives (HFS+, NTFS, EXT#, APFS). No you can’t pool arbitrarily sized drives, but you can’t with any of those either. And yes, you lose data if your single drive fails, but you also do with any of those.
I feel like you're trying to get into an argument about which filesystem is better, rather than simply acknowledge that ZFS doesn't actually solve the problem under discussion.
I disagree. ZFS + backup autorecovery solves 99.9%+ of bitrot cases. Time Machine already is the easiest to use fully automatic backup software, ZFS already notices bitrot (and corrects for it in mirror/raidz configurations, but that’s neither here nor there). It’s not a hard logical (or technical) leap to assume that had Apple moved to ZFS, it would leverage Time Machine backups to restore corrupted files automatically. This does actually solve the problem under discussion (or at least, improves it for the average person).
Without ZFS (or some other automatic checksumming), Time Machine (or any other automatic backup solution of fixed size) backups with a good copy of data will eventually be updated with new corrupt copies of the data, and then aged out when the backup target runs out of space. The solution doesn’t have to be ZFS; my point was that it could’ve been, and very nearly was.
