Glancing over some of the basic stats right now, Hunter and O'Day seem to be the "closer candidates" if Showalter ever decides he's going to make a change.
Hunter: 2.09 ERA, 0.80 WHIP, 7.23 K/9 IP, 7 HR, 4.75 SO/BB ratio (38 SO, 8 BB), 47.1 IP
O'Day: 2.13 ERA, 1.08 WHIP, 9.24 K/9 IP, 4 HR, 3.55 SO/BB ratio (39 SO, 11 BB), 38.0 IP
Johnson: 4.02 ERA, 1.31 WHIP, 7.14 K/9 IP, 3 HR, 2.29 SO/BB ratio (32 SO, 14 BB), 40.1 IP
The WHIP seems to be the most significant difference, although Hunter's extra HR's given up may be a concern.
(None of this changes my earlier opinion that the bullpen shouldn't have so many defined roles to begin with.)
Nice article by Jeff BTW. It's a bit surprising that he's throwing a higher % of first pitch strikes, given he seems to have more issues with walks than in the past. Food for thought:
Johnson and walks vs. IP:
2010: 5 BB in 26 games / 26.1 IP (~ 5.1 IP per walk)
2011: 21 BB in 69 games / 91.0 IP (4.1 IP per walk)
2012: 15 BB in 71 games / 68.2 IP (~ 4.2 IP per walk)
2013: 14 BB in 43 games / 40.1 IP (~2.2 IP per walk)
I certainly hope JJ fixes his problems and gets back to being a feared closer.