It's funny that you say that after calling Hanrahan mediocre. Balester's younger, but he's had a very mediocre year at AAA. None of his peripherals indicate that he's ready for the big leagues.
You have to keep in mind that Balester has only made 9 starts in AAA and he has done reasonably well. He pitched very well in AA prior to getting promoted.
Numbers in AA: 98.2 IP 103 H 47 R 41 ER 9 HR 25 BB 77 SO (3.74 ERA, 1.30 WHIP)
Numbers in AAA: 45.2 IP 45 H 25 R 22 ER 2 HR 22 BB 32 SO (4.34 ERA, 1.47 WHIP)
Overall: 144.1 IP 148 H 72 R 63 ER 11 HR 47 BB 109 SO (3.93 ERA, 1.35 WHIP)
Those are much better numbers than pretty much every other starter in our system (upper levels) and the bonus is that Balester is only 21. The organization thinks highly of him and I'm sure he will seriously compete for a starting spot in Washington next year.