easy pickings vs piece of cake

easy pickings

noun
  • Something easily acquired or stolen. 

piece of cake

noun
  • A job, task or other activity that is pleasant – or, by extension, easy or simple. 

  • Used other than figuratively or idiomatically: see piece, cake. 

How often have the words easy pickings and piece of cake occurred in a corpus of books? (source: Google Ngram Viewer )