Osuna has thrown 4 times in 5 days.
With Gibbons managing, it would be hard to make a convincing argument that Sanchez is less likely to get hurt in the pen. He will be run to the ground in the pen. At least Gibbons has been fairly consistent at keeping him at around 100 pitches as a starter.
I understand Shapiro's argument, but without more science based fact about whether it actually helps a starter remain healthy, it's kind of pointless. With how hard Sanchez throws, he could get hurt at any moment. There's really no way to predict it or prevent it.