The Red Sox have been drafting high-upside HS talent for years. The reason why the Sox farm system is "middle of the pack" is because that strategy gives you better overall talent at the cost of more development time, thus most of the upper-tier talent the Sox have amassed is in the lower tier of the minors. Any self-respecting talent evaluator will tell you that the Sox are loaded with high-impact talent, but they can't be ranked any higher because that talent will take a while to reach the Majors.
Oh, and of the two links posted to "Rankings list" one is from before the 2011 season and the other one is Bleacher report, which is completely unreliable.