After cloning my Mac, why are my time machine backups so slow?
I found this answer on Apple's forums (excerpted below) after much searching. After applying the solution below, incremental backups only take a few minutes after the first (very long) backup. Looks like my suspicions were correct about FSEvents not working. I suspect that something about the disk cloning process-- both for me and for the poster excerpted below-- messed up FSEvents logs and a rebuild was needed of those logs. 

Sharing the solution here to help others: 


  I was having the same problem (hours-long backups of a few MB) after
  using CCC to transfer my files to a brand new SSD. I don't think the
  SSD has any problems, as it is brand new, and the disk verification
  checks out. After hours of searching online, disabling Spotlight, and
  using TimeTracker to see if 100000+ files were actually changed (they
  were not), I found the following seems to work:
  
  
  Delete /.fseventsd on your startup drive or move it to another location:
  
  
  sudo mv /.fseventsd /.fseventsd.bak
  
  
  Reboot
  Start a Time Machine backup
  
  
  Afterwards, the first time TM is run, it took much less time to reach
  "Finishing Backup," though it stayed on that step a really long time.
  However, subsequent TM runs are back to normal.
  
  Source: http://www.ehmac.ca/archive/index.php/t-100787.html
  
  (Posting here so more people can find the solution; it took me several
  hours to find that one.)