I think Billy has it right
The point is, Barret's is not Garnet's song, good song or not. If YOU write a song and everyone wants it, that's reason enough to keep singing it, if you feel obligated.
But Garnet should not feel obligated to sing this song any more than he should feel obligated to sing Danny Boy or the Unicorn, or Amazing Grace.
It's doubly hard for him because people EXPECT him to carry on his brother's reputation. He loved and admired his brother and is very public about that, but he IS a living , growing musician in his own "write".
Give the guy a break! He's carrying TWO albatross-es and just wants to be appreciated for who he IS.

If you have not heard him live, check it out.. and DON'T ask for Barret's Privateers

Best- Julia