Really makes you wonder doesn't it? Each of the past 2 years has looked good before losing it on his promotion to the next level. Was everyone wrong about his skill set? Does he wear down and need more strength? Does he just take longer to adjust to the new level than we'd like?
2019 is an important year for him, to be sure.
To try to answer your questions with my thoughts:
1.) wrong about skill set? I don't think anyone has been wrong about his skill set. Shortstop defense Solid hit tool who will have more power than Dee. Needs to keep getting stronger. I think that's been the report all along.
2. ) Wear down? This is certainly possible as there has been a second half swoon the last two years and also in the previous years.
3.) AAA is the first time he's struggled to adjust to a new level. He hit right away in E-Town in 2014. He hit right away in Cedar Rapids in 2015. He hit right away in Ft. Myers in 2016. He hit right away in Chattanooga in 2017 and 2018. AAA isn't easy, and it was his first midseason promotion. So, combine him being one of the youngest players in AAA with his normal 2nd half struggles and we shouldn't be surprised he struggled in his transition to the highest level of minor league baseball.