Of the so-called four major professional sports leagues in the U.S., MLB's draft is by far the hardest to assess.
Even the best players won't make their big league debuts for two or three seasons. The ones who get fast-tracked are more than likely to be short relievers—guys who aren't typically drafted high enough to garner national attention.
Mike Trout didn't become a full-time MLBer until nearly three years after his draft date. Bryce Harper wasn't down quite two years. And these are all-time outliers.
First overall pick Mickey Moniak probably won't be in a Philadelphia Phillies uniform until 2019, and he might not get there until 2020.