I'd be surprised to see him this season, but I was surprised to see Robles up last season. Soto missed much of last season with injuries, and without that he almost certainly would have been in Potomac at the end of last season, and either there or Harrisburg at the beginning of this one. So him getting to AA now isn't as much a shocking rise as much as it is him making up for the lost time of last season.
Like others have said, AA is a different animal to the Carolina League. I saw him at Hagerstown and he did fine with same-side breaking pitches there, but a Sally League show-me curve is not the same thing as breaking pitches with bite and location that are coming off mid-90s fastballs, which you start to see a lot more of in AA. I do think AAA is useful, especially for unusually young prospects, as you face older pitchers who have a few more tricks up their sleeves.
The defense is what it is. When I saw him in April, he looked like he was covering more ground in the OF than when I'd seen him before, but I don't think he has the arm for RF in the majors. Assuming the improvement I saw was real, he can probably stick in LF with a good defensive CF (like MAT or Robles, once he finishes developing) next to him.