An Argument For Happy Birthday

Should the song Happy Birthday To You be in the public domain?  Ben Sisto at freeculture.org thinks so. He meticulously documents the copyright history of the song.  Ben points out that the song is a derivative work  using folk song lyrics and combining them with the melody to the song Good Morning To All written by and copyrighted to Mildred Hill in 1893.  The original lyrics to GMTA were written by her sister Patty Smith Hill.  Warner Music currently owns the copyright on Happy Birthday which expires in 2030.  As techdirt mentions, the song generates about $2 million per year.  I thought that Paul McCartney had the song in his publishing arsenal, but it turns out it is in the hands of the Patty and Mildred Hill estate.  McCartney's MPL does own the rights to the Christmas Song (Chestnuts Roasting On An Open Fire).  Would love to know what that generates in royalties each year.