At the point Barnes entered the game, the Sox had pitched 5 innings and still needed 4 innings and 12 outs. I think the 6th is more middle inning than late.
When you say, "middle inning fodder," you essentially mean not worth much, and the problem with that idea is that too many in the current bullpen could be included--Tazawa, Barnes, Ross, Abad, and maybe even Buchholz who is probably a better starter than reliever. That leaves just Kimbrel and Ziegler who are reliable or semi-reliable.
Let's not forget that most on this board, probably including you, also believe Farrell stays with his starters too long.
So, when you add all those things up--limit the starters, use the bullpen early and often, just two reliable (maybe three) relievers--you have a problem. Nevertheless, it is usually Farrell who is blamed when the pitching--some combination of starters and relievers--gives up too many runs.
I on the other hand see managing this team's pitchers as akin to a high wire act, trying to find the right balance between what is available and what is needed.