I'm not dense
I can clearly see that the Pirates have guys like Starling Marte and Gerrit Cole make huge impacts on this Pirates team. The Pirates farm system has been highly rated for good reasons. However if we just look at the 2014 season the Pirates have gotten almost no impact from the farm this year.
Let me qualify this by saying I don't count Vance Worley, Jeff Locke, etc for the purposes of this post. If you want to include them that's fine, but for my purposes I'm just talking about guys who were in the top 30 Pirates prospects according to Baseball America. Here's the list.
Looking at that list the only guys who have impacted the 2014 team are
I'll address these players one by one
64 G 249 AB 241/308/349 -2 Defensive Runs Saved
Exhibit A in my case is the production of this uber prospect. Polanco hasn't excelled in his first go round in MLB. His defense has been shaky and his offense hasn't been much better than Travis Snider/Jose Tabata. I don't say these things to disparage the kid, but clearly there's been an adjustment period for Polanco. I think it's safe to say we expected more. There's no doubt that this kid has the tools to be a great player, but his 88 OPS+ and his 0.1 bWAR make him basically a replacement level player for the 2014 Pirates thus far.
13 G 10 GS 64.2 IP 5.01 ERA 72 ERA+
Cumpton was expected to be a depth option for the rotation when the season started, so his performance isn't all that bad in that light. It's easy to see that any game Cumpton started was supposed to be started by Taillon if he was healthy. It's a fair point, but that doesn't put any wins on the record. The fact is Cumpton overall wasn't a factor in adding to the 2014 playoff push.
21 G 72 AB 278/316/375
Sanchez was just a fill-in for Russell Martin, but while he was the starting catcher he showed why the Pirates were wise to sign a veteran backup. Offensively he was fine for a catcher, but we all remember cringing whenever he had to make a throw from behind the plate. Sanchez had some big hits early in the year, but the team lost with him as the starting catcher. That's not all on him, but he certainly didn't help the pitchers as much as Russell Martin or even Chris Stewart.
19 G 31.2 IP 5.40 ERA 67 ERA+
Pimentel has been ok in a few appearances, and horrible in a few more. I think he has a shot to make the starting rotation in 2015.... but he hasn't helped the team make the playoffs in 2014.
Taylor impacted the team in that he was the PTBNL in the Ike Davis deal. Ike has disappointed to be sure so we have to say Taylor impact was minimal on the 2014 team.
If you want to bring up Jaff Decker, that's your prerogative, but clearly neither he or any other players from the farm system made a difference in 2014The season still has 32 games, so there's still time to make an impact.... but the Pirates haven't been improved by any of their prospects this season to this point.
So what's my point....
I'm not saying the Pirates prospects haven't made progress this year, but coming off a playoff year in 2013 that saw the Pirates get big contributions from Starling Marte, Gerrit Cole, Dillson Herrera(turned into Marlon Byrd), etc... the 2014 newcomers haven't made much of an impact at all. The Pirates counted on internal improvement to carry the team back into the playoffs this year, they simply haven't gotten the kind of impact they needed to justify not improving the team.