This is not on Shelton. If you overextend the only good leverage pitchers that you have, they get tired and/or hurt and then you are totally screwed.
This is the domino effect of 1) winning the bullpen game yesterday by using the leverage relievers and 2) Ben Cherington not having enough usable depth.
You just can't have guys like Heller on the team and not use them or expect to win when you do. And Ben Cherington's Pirates have 2 -- him and Heller. There's not much Shelton can do because he has to be cognizant of the longer view.