Along with what Nardis says, forget whether you think these guys are doing well now. Think about the future. Let's say these guys keep performing as well as they are in their current positions. That means our farm has produced a brilliant starter, a LF who can hit 30 HR/year. Great! That's awesome. The starter is big, and the LF, while not someone to build a team around, is a very solid player to have at the position.
Now let's look at the others. We've produced a closer with a 4.00+ ERA, two bench players (one of whom is a good fielder and can't hit, the other is an OF who hasn't drawn a walk yet, so I don't think he'll bat .400 in a season), and some good pen pitchers. Add on to that fact that pen pitchers are NOTORIOUSLY streaky AND that they provide little value compared to a starting pitcher, and you start to realize that we haven't produced very much. We just have some guys who are performing well and keeping our team afloat along with one star (in his first year of starting) and another good player (also in his first year of starting).
Now, the icing on the cake. What if even half of these guys perform worse next season? Odds are it will happen. It's certainly happened with all prospects we've ever had and I'm sure the same goes for most other teams' prospects. Then what have we produced?
Long post, I know, but my main point is that you don't base the story of our farm system off of a half-season or less from a few prospects. And even if you do, it's not that impressive of a story.
P.S. I hate to even imagine it, but think about who we would replace someone like Paulie or Alexei with if they went down. That's when things get really scary.