Not quite right - you absolutely can expand raidz vdevs by replacing the disks one at a time. What you can't do is increase the "width" of the raidz, or seamles

Not quite right - you absolutely can expand raidz vdevs by replacing the disks one at a time. What you can't do is increase the "width" of the raidz, or seamlessly rebalance data between multiple vdevs.