I wasn't aware that anyone thinks ZFS is no better than ext4. Surely the interest in developing Btrfs and Bcachefs, with features obviously meant to compete wit

I wasn't aware that anyone thinks ZFS is no better than ext4. Surely the interest in developing Btrfs and Bcachefs, with features obviously meant to compete with ZFS, would suggest that mostly people think it is? And you also have Canonical adopting ZFS outright, and Red Hat working on improving XFS as an alternative file system.