Zack Wheeler is the big deal here.
Wheeler was dominant: 7 IP, 3 H, 1 R, 1 ER, 0 BB, 8 K. He threw 75% (!) of his pitches for strikes (68 of 90), a season-high.
In the process, he lowered his ERA to 1.88, which is fourth in the Eastern League and reclaimed the League's strikeout lead (60) while maintaining the lowest batting average against (.169) and the highest strikeout rate (10.25). The eight whiffs were one off a season-high, and walkless start was his second. He's fanned at least seven in each of his last four starts.
He's been crazy good in his last two outings: 15 IP, 5 H, 2 R, 2 ER, 2 BB, 15 K. He's very, very close to being ready for AAA, but his time in AA has helped him enormously. In April he walked 13% of batters while in May, that dropped to 7%. He's clearly getting better. That's the big reason to keep in AA for another start or two or three, or four. There's no reason to rush him to AAA when AA is helping him.