Yes, but that doesn't do the job that a fsck implementation does. fsck is something you stuff into your initrd to do some quick checks/repairs prior to mounting

Yes, but that doesn't do the job that a fsck implementation does. fsck is something you stuff into your initrd to do some quick checks/repairs prior to mounting, but btrfs intentionally doesn't need those. If you need btrfs-check, you have probably hit either a catastrophic bug or hardware failure. This is not the same as fsck for some other filesystems. However, ZFS is designed the same way and also has no fsck utility. So whatever point was intended to be made was not, in any case.