The problem with this line of thought (just my opinion based on what we've often heard when these types of players are brought in) is that they're not brought in to specifically help in the win-loss department. When Wren went out and got Billy Wagner, he wasn't concerned whether his numbers were reflected in the number of wins - it just so happened that he did help in that department. Wagner was brought in for one reason - to show Kimbrel what it takes during camp, on off days, on days he's not used, at times he hasn't seen action for 4-6 days to remain sharp and ready when he WAS needed. The same thing was a big part of the reason you bring in Grilli and Johnson for the most recent group of pen arms. KJ and Gomes were brought in to help the hitters understand the extra preparation it takes to be helpful when you're not an everyday player so that you might be able to help as a pinch-hitter or short-term injury replacement for one of the regulars. A. J. wasn't brought in to produce - it just worked out that way. He was brought in to help Bethancourt understand the important details of how to run Pitchers' meetings, how to call games, when to go out and talk to Pitchers to calm them down, help him understand how important it is to understand their mechanics so he might be able to help them make adjustments in the middle of an inning without McDowell having to come out, etc..
The only one of the veterans that was brought in for 2015 that was expected to produce in any form was Markakis - the other guys were brought in to be teachers or tutors in the hope that the young players might gain some knowledge from a voice that they identified more with since they didn't have the title of Manager or Coach tied to their names. I think most organizations are big believers in those types of guys when they have young teams. The problem with last year's team is that it was taking the kids longer than expected to make those adjustments and those veterans were performing better than expected and HAD to be played or the record would've wound up much worse than it did. I shudder to imagine what the record might've been without KJ and A. J.'s production and without Grilli and Johnson in the pen before the deadline when they were the ONLY guys in the pen that could get anyone out. The lack of offense was obvious, but how much worse might it have been with Eury Perez in CF, Todd Cunningham in RF, and Terdoslavich in LF all year?
I was one of Fredi's biggest haters when it came to playing A. J. instead of giving Bethancourt regular ABs and experience handling the staff, but wasn't there to see what was happening during workouts/bullpen sessions on throw days/during Pitchers' meetings. Maybe he really just wasn't learning anything from watching A. J. do those things. If so, I completely understand why he wasn't being played. Same thing with the other guys - if the Coaches and veterans keep trying to explain to you why you're struggling (Peterson's struggles against LHPs/Garcia's defensive struggles, the inability of the young SPs and RPs to throw strikes somewhere that weren't belt high over the center of the plate), you have little choice but to play somebody else until you find someone that can do those things.