The only real flaw in Baez's offensive game to this point has been a low walk rate (just 6.2 percent on the season) that risks being exposed against more advanced pitching. But as Arguello points out, that walk rate has been steadily improving over the course of the season as Baez works on his approach. That's very good sign for his development.
Arguello expects the Cubs to accommodate Baez and allow him to play shortstop full-time in Double-A, but also suggests that he could move around the diamond to allow fellow prospect Arismendy Alcantara to play there as well. Baez has the tools to play both second and third base successfully, but has not always displayed a willingness to do so, as was evidenced by his time in the Arizona Fall League this past year.
Baez has earned this promotion with his bat, and even more so if the reports coming from the team on his improved maturity and willingness to adjust are true, as those were bigger red flags for his development than any physical issues. Still, a mid-season promotion marks a change in philosophy in the Cubs handling of Baez after they were extremely cautious with his assignments at the start of his professional career.
Still just 20-years-old, the Cubs could have been patient with Baez and had him spend an entire year at each minor league level and still had him in the majors by the time he was 23. This move suggests that there has been a change in their thinking regarding Baez's development, likely motivated by his on-field play and his willingness to work with the organization, particularly in the area of plate discipline, which the Cubs are stressing to young players as a developmental philosophy.
It's still too soon to tell if Baez will be able to stay at shortstop, but it's clear that he will get every chance to do so, especially with the team's selection of Kris Bryant at number two in the draft this season now blocking his path.