Well rsync is like all Unix tools: super helpful, super powerful and extremely dangerous if not handled with care.

After upgrading from High Sierra to Mojave, Time Machine backups to my WD Mybookliveduo were very unreliable with frequent verify failures. Also it was exceedingly slow.  Am now doing duplicate backups.  One to a USB drive via TM.  The 2nd is with rsync to the WD drive that I am experimenting with.  Rsync B/U is very fast.

Also I upgraded the out of date version of rsync the ships with macOS.

RSync the old is still new...