I thought the exact same thing as I was watching the game.
The opposing batter has terrible numbers against Kimbrel, but nonetheless, Barnes was dealing and there were no runners on base, much less in scoring position. I would have left Barnes in.
I'm not saying that that's the reason that Kimbrel blew the save, but I would have saved Kimbrel the pitches and the 1/3 of an inning.
Interesting decision.