I admire Cubs fans (I am one myself) for their positive nature, but history can tell us some things we may not want to hear. Just ask Nate Silver.
I'd like to note two seemingly reliable ways to gauge future success for position players in the major leagues, though I admit I do not have the scientific data to back it up. They are: A player who has not established himself with a breakout year in the majors by age 25 will probably not become a star of any magnitude. And if a player toils much at all in the minors, he likely will at best have modest success in the majors.
I did some quick research of the minor and major league statistics of 13 of the Top 15 vote getters on the 2012 Hall of Fame ballot (I did not include pitchers Lee Smith and Jack Morris, since we are talking about position players). They are: Barry Larkin, Jeff Bagwell, Tim Raines, Alan Trammell, Edgar Martinez, Fred McGriff, Larry Walker, Mark McGwire, Don Mattingly, Dale Murphy, Rafael Palmeiro, Bernie Williams and Juan Gonzalez.
Now, other than Larkin, who is in the Hall, I think we can agree that not too many of these guys are likely to get in. Perhaps Raines, and maybe one or two more down the road in some fashion. McGwire and Palmeiro are scarred by steroids, but that doesn't really factor in here, since they almost certainly weren't doing them in the minors or early in their careers, which is what we're measuring here.
So what we have are a number of very good players, which is all we should have the right to expect as we see the likes of Castro, Rizzo, Baez, Soler and Almora in the majors or working toward that goal.
But keep in mind that all of the previously mentioned 13 players posted at least an .800 OPS season by age 25, with the exception of Trammell (who posted a .775 and 4.8 WAR by age 22; Larkin, who attained a .776 and 7.0 WAR by age 24; and Martinez, who came to the majors late - one of those rare future stars who was not established by age 25). These statistics are, of course, assuming a full season (at least 502 plate appearances, although there is one instance where I allowed a season of a few appearances short of that to qualify). In addition, most of these players dominated in the minors with few instances of any sustained struggles, with many being on a fast track to the bigs.
It also should be noted that most of these players exhibited strong plate discipline, at least according to their stats.
The point here is, it's probably no small deal if say, Baez struggles this year at Daytona. A full season of struggles just doesn't happen very often in the minors, even to a 20-year-old, if they are destined for big things. Also, all those players who have had mediocre minor-league careers who we are hoping suddenly emerge - that is also rare. And to say Castro "is still so young" or "give Rizzo time because this is his first full season in the majors," well, not so much. At 23, Castro needs to take a step or two up within the next couple years to project as a perennial star (which very well could happen) and the time is now for the 24-year-old Rizzo (it's actually very unusual for a first baseman who has not played a full season in the majors by his age to go on and be a significant star).
And Brett Jackson? I think Nate Silver would tell you that that ship has sailed.