Yes it is certainly true that Diskwarrior, Techtool Pro and Drive Genius cannot perform a Disk Directory rebuild on APFS because Apple has not released the necessary info. TTP and DG use
fsck
, the same as Disk Utility First Aid which is the only APFS directory checking tool available, and free!
OTOH one of the big benefits of APFS is that it is less likely to get corrupted.
Is there a typo in your sentence
"The fewer APFS backup disks you have, the greater the risk that you can lose data" ? Did you mean the
more APFS backup disks the greater the risk?
Are you saying that your TM disk that had a hardware failure last week was APFS, and if it had been HFS you could have recovered the data from it with DiskWarrior during its death throes ? Possibly, but my experience was that Diskwarrior et al were not useful for proper hardware failures. They were more useful for repairing the Directory structure of physically healthy disks which had some corruption of directory. Proper hardware failures is one of the main reasons for backups.
BTW on the subject of APFS and HDDs I have been having an interesting discussion about speed in
this thread. Bottom line I see exactly same speed of HDD backup to HFS and APFS. Doing some more tests to try and discover why it is widely believed APFS on HDD is slower.