I think the ZFS changes were due to needing a way to allow qnap systems to expand zfs pools. The raidz expansion features in openzfs probably took too long for qnap to wait.
I'll be snide and say it: "OpenZFS" and "stable" rarely belong in the same sentence (even though they seem to have a true 2.2 LTS these days).
OpenZFS released the zpool expansion as stable last year. Hopefully QNAP is charting a path to allow their users to migrate from their fork to OpenZFS, though of course these kinds of things take time to develop. I would be really worried if they are diverging further from OpenZFS rather than converging.