Gregory hasn't been great, but he's calling the defense now - his issue is athleticism, he apparently has some valuable football smarts. Which frees them up to use their LBs based on their ideal roles, instead of having to force Hightower onto the field in all situations because he's the next guy up who would call the defense, which means even though Gregory himself isn't an elite athlete, he enables the defense to be a lot better than they otherwise would be.
If he can really call the defense, then he's gonna be on the field for pretty much the whole rest of the season.