I disagree that the Sox are desperate for a reliever. Our bullpen isn't the best in MLB, but it's solid. We have a good rotation to take into the playoffs and 4 potential backline starters with relief experience to pad the playoff roster (although of those, the only ones I'd absolutely trust are Velazquez and Johnson)
On the high leverage side, I have no reason not to trust Barnes and Kimbrel to get it done on the big stage, both have been very consistent this year. Like it or not, Barnes is a fine setup man and has done some good work this year.
With Velazquez probably a lock for the playoff roster and the need for at least one emergency starter, that only leaves maybe as many as 4 slots for all of Kelly, Brazier, Hembree, ERod, Wright, Thornburg, Pomeranz and whoever else distinguishes themselves down the stretch and in September.
The point is we're already going to have a fair number of pitchers on the outside looking in as it is, some of which would be deserving of playoff spots on many teams. There's always the possibility of upgrading with one more high leverage arm, but it's not an urgent requirement as long as Kimbrel and Barnes stay healthy. No reason to force a trade here.