The Major League Baseball draft is a different kind of event than those player drafts conducted by the NFL, NBA and NHL.
Those three sports all expect many of the top picks, along with several others, to step in and contribute right away. Even the best MLB draftees take at least a year or two to develop, while those in the NFL and NBA can play as rookies and make major contributions. The same holds for the most elite players drafted into the NHL, but many more of them need seasoning.
However, that does not mean the MLB draft is a hit-or-miss affair.