I disagree. The Civil Wars pretty much did the backing vocals and added next to nothing on the track
My speculation is they wrote a big portion of the track but Taylor's label were never going to allow a vocalist as amazing as Joy Williams
to share lead vocals on that track, that's for sure.
Great news for The Civil Wars, though - their Grammy record is now nominated 3 times, won 3 times. I just hope they can sort out their differences, the music world needs such talent to be a part of it.