You are right, the defenders don't get any style points for the way they make the plays. However, if Jackie is really that much better than other defenders, he will get to balls that other defenders do not get to.
How do you know how well Jackie is doing, relative to the other centerfielders this season?
Also, and more importantly, don't read too much into a 1/2 season's worth of defensive metrics. One or two missed balls, which Jackie has had this season, can greatly sway the numbers in such a small sample size.