There are, with few exceptions, no two-pitch starters. The challenge of facing a MLB lineup three or more times without much variation in offering is too daunting, the opponents too talented. It’s what makes scouts look at Justus Sheffield and see a future reliever, using his fastball-slider combo to excellent but condensed effect. Good relievers are important, of course, but pitchers who can capably handle 5+ innings will always provide their team more flexibility than those that go 1-2. Naturally then, the Mariners want Justus Sheffield to be a starter. If their top-heavy rapid rebuild is to be successful, they likely NEED Justus Sheffield to be a starter.