I watched Johnson's start on MiLB TV. He's solid 91-93 with excellent movement on the fastball away from right-hand hitters. His slider is a plus plus pitch with good downward movement. He also showed a decent curve, straight change, and because he pitches for the Sox, a cutter. He pounded the lower portion of the strike zone, rarely falling behind guys. Only a few balls were hit anything close to hard off him and Jacksonville is good. Yelich, Marisnick, and Cox are probably better than the guys playing their positions for the Marlins right now. I think if he had to make an emergency start right now, Johnson would hold his own because he's not afraid to pitch to contact. Seems like a number three or possible better because his command is improving. Also, gets it and throws it. Has a good competitive streak.
The only hitter that Birmingham has who looks like a future major leaguer is Thompson. He hit a couple of very hard outs and generally looks like he belongs. His swing is shorter than it was, but needs to tighten up a bit. Dan Black can hit, but he is the slowest player I have ever seen.
Witness to the agony ('76 Sox season tix) and the ecstasy (2005 World Champions!)