How does Time Machine restore backups from APFS volumes?
Time Machine at the moment of writing doesn't support APFS for the backup destination (see this), while it can backup FROM an APFS or HFS+ volume. That's because the AFPS filesystem doesn't support directory hardlinks, which Time Machine heavily relies on.

Probably Time Machine needs to be rewritten to take advantage of the features you mentioned, which is something that can happen in future versions of macOS.