As TT said in the other thread, if he's actually getting called up today, that would imply he's not here to actually start. Or maybe he's joining the team today but not formally rostered until the next rotation turn comes up?
Anyways, he's not a floor prospect where he needs to show incremental steps until he's big-league useful. He's a "maybe someday his command will snap into place and he becomes a superstar" prospect. Which does happen sometimes for pitchers. Maybe it's happened with him. If it hasn't, if he's the same guy he was at AAA last season, he's going to get abused by MLB hitters.