The tough thing about projecting in Baseball is the uncertainty Rounds 1-40. In other sports you have more knowledge of what you're getting.
In comparison, in the NFL, you know a first round guy should be a super star or a QB... QB's are the biggest question marks. 2nd-4th rounders will probably be decent players to stars, and 5-7 rounders will probably be around the next 3 years but there are no guarantees they will contribute much. They are your NFL lotto tickets.
Comparing that to baseball, a first round pick in baseball is more like a 5th to 7th rounder in football. They will probably make it to AAA and you will hear about them for the next several years but there is no guarantee they will really ever contribute. Everyone after the first round is an even bigger question mark.
In the NBA, you pretty much know what you're getting from the outset. Unless your the Spurs, the second half of the first round through the second round are gonna be role players.
MiLB and MLB baseball is such a crap shoot in comparison...
The main problem with the baseball draft is that the level of competition is varied. A guy like B.J. Garbe might look like a future major league all-star because he is playing against high schoolers in the state of Washington and it is virtually impossible to extrapolate from that performance.
When I watched Garbe in rookie league ball (Elizabethton vs. the Danville Braves) I could tell he was limited in four at bats.Now, instead of inept high school pitchers he was facing drafted players only and you could see he did not have the bat speed. At the same time, you could see that Tim Spooneybarger had a future because he not only had a draftable fastball, but could change speeds with control.
Spooneybarger was a 29th round draft pick.BJ Garbe the 6th overall.But it was Tim that was in the major leagues 2 years later and Garbe never got above AA.
What I think major league baseball should do is draft from the Rookie leagues.Instead of drafting in June, once a player is eligible for the draft they would be assigned to a rookie league team.THe major leagues would pay them to play from a common fund.Then, at the conclusion of the short leagues, the teams would draft based on the scouting a league were the players are all of a "draftable" quality.
I get there are some things that would have to be worked out.For example, most of the top level players would refuse to play and I have actually talked to a couple of former major league executives and htey hate the idea. Their position is that they have their own draft secrets and don't want them exposed.For example,the Twins drafted Justin MOurneau in the 3rd round the year they drafted BJ Garbe.
But, in the end, what would have happened is that instead of drafting Garbe 6th overall and giving him $1.5 million, they would (or could have) selected Mourneau there and given him the bonus and Garbe would have been a later round.