Look at the the games he's blown. If he had only blown 1/2 of those games the Stros would be challenging the Mariners for 1st place. As you know Pressly has been really bad.
Blown saves in games the Stros lost plus straight L's: Pressly 6 Hader 4 Montero 3 Abreu 2 Martinez 2 Scott 2 Dubin 1 eta1: our save% is 6th worst in MLB eta2: while poking around on B-R, I looked at quality starts. The Stros are tied with Baltimore at 11th in MLB (41%), league avg is 38%, Cleveland is a weird outlier at 29% (tied for 4th worst) despite having the 4th best record in baseball. eta3: bullpen inherited runner scoring% is 6th best in MLB, and they have the fewest runners inherited in MLB (thought that was interesting, wouldn't have guessed...although maybe I should have, it speaks to Espada leaving pitchers in too long and by then the damage is done)
So, one player has 50% more failure overall than the 2nd worst... but when he's in a save situation, he's damn near perfect.