it doesn't get 'overused' so much as you just have to keep reach lower and lower in the pitcher barrell for innings until you have to start using guys who can't get anyone out like Hill/Misiewicz.
It's always just a mattter of where the next level of quality is in your system. If there had been good staters at Toledo in the pipeline, they would have been pitching in those games instead of having BP days. But we've already pulled all the starters out of the Toledo rotation who had any chance of surviving ML hitters (Faedo, Olson, Wentz). Wentz wasn't up to it, Faedo got hurt, Olson is hanging in there. Holton, Englert, Cisnero, Vest, Alexander, White - are all better pitchers than any starting help available in Toledo so they got the innings up to the limit they are available.
If 3 starters were not on the way back shortly the next step would have been bring back Brieske and to stretch out T. Alexander again, even knowing he's been more effective as a reliever.