The Cubs have a lot of mid 90s pitchers in their system, but most of them have been moved into relief. In addition to Black, you have Edwards (perhaps temporary), Paniagua, Francescon, Perakslis and Thorpe. Most of them have had command problems, which probably is the reason why they are no longer starting. They have also brought in young pitchers from the outside that are also mid 90s pitchers, the best of which have been Ramirez, Grimm and Rondon.
To me, it looks as if they have decided to take top hitters with their highest picks, and then bring in several high velocity, low command pitchers in the hopes that they can overcome their command problems at least enough to be effective relievers, and perhaps even enough to be good starters.
But in addition to that, they are also bringing in a lot of high command, lower velocity pitchers in the hopes of developing Hendricks-like starters. All part of the "attack pitching with volume" strategy.
I would expect that they will draft three or four high velocity pitchers in the last 20 rounds, in the hope of striking gold.