Edit: The cheeseisblue succinctly and correctly points out..
That’s a misleading summary. As he says several times in the article, the Pirates have a lot of high upside players who are just too far away to give higher grades to. There is a lot of potential in the group, but they’re too far away to accurately judge or grade. That was my interpretation of the article, along with the thought that the Pirates have a very difficult system to grade.
Sickel's posted his top 20 Pirates Prospects just in time for Christmas! Unfortunately, the list doesn't make the best Christmas present, at least in my eyes. Elite talent up top, but John doesn't really buy into the Pirates depth.
For comparison, the following farm system's B- or better prospects.
Orioles - 7
Brewers - 9
Dodgers - 10
Nationals - 13
Twins - 13
Cardinals - 13
Red Sox - 15