The reasoning for running a scrub after an unclean shutdown is not to catch corruption of the filesystem structure, but to catch data corruption resulting from

The reasoning for running a scrub after an unclean shutdown is not to catch corruption of the filesystem structure, but to catch data corruption resulting from the RAID5 write hole. If you're not using RAID5 or RAID6 for metadata, the write hole won't affect the filesystem structure and there shouldn't be any issues for btrfs-check to find.