De Los Santos is on the 40-Man Roster so the Rangers are protecting him as much as possible. I'm not sure they have to worry about keeping him under the radar. Although he has shown some promise in the past he hasn't progressed as he should have. He's been in the system for 7 years and has been unable to get to a level higher than AA, which he reached last year and didn't do too well.
He made 6 starts at Frisco earning a 1-3 record with an ERA of 8.04. In 28 IP he gave up 27 hits and 17 BB and allowed 25 runs. The bright spot is the 38 Ks but the rest of the stats are just as disappointing as the others. I think control is his biggest issue.
Miguel is 23 and will turn 24 in July. If he's going to fulfill the expectations he's going to have to get it done soon.
I noticed that he won Pitcher of the Week in the AFL but according to baseball-reference.com he only pitched 3 innings. Maybe their info is incomplete.
http://www.baseball-reference.com/minors/player.cgi?id=deloss001mig