I think that sometimes explosiveness can be mistaken for pitchers who get out too early with their upper-body.
I would say that Trevor Rosenthal, Justin Verlander, Jose Fernandez, and Felix Hernandez are all explosive, but they all also have very clean easy mechanics.
My son pitches at the Division II level in college, and he’s had a variety of team pitching coaches who’ve tried to get him to come over more with his upper body, extend more, create a little more explosiveness in his delivery.
The other day he had a pitching lesson with his old pitching coach. Within 10 minutes he fixed/took out most of this stuff from his delivery, and his location, movement, and velocity all jumped.
The coach reversed this stuff, making him get back, stay back over his back leg, keep his shoulders level, drive down slope with a nice push before foot strike. When his hips opened, he wanted his shoulders back, creating separation and also extension because his arm could extend against the quiet upper body platform that was created.
By doing this he created arm speed/explosiveness with enough force that after the ball was released, the momentum pushed his back leg up and over, his arm driving all the way through.
The change was dramatic, moving from something more violent and less controlled to a delivery that looked collected, smooth, relaxed, generating great arm speed and a ball that exploded out of his hand.