Yeah, unpopular opinion but Stone Cold isn't that amazing. The lyrics are cliché and it sounds a tad bit try hard for me. I don't believe that Demi has felt any of the feelings in the song.
The song honestly feels like she just wrote it to get a GRAMMY nom. Father and Yes are the better ballad(-esque) songs on the album. The better single would be Yes.
Plus, releasing a ballad in 2016 is sorta a no go. Adele is not leaving, and she owns the ballad game.