The Mariners roster heading into the season is pretty well locked. Sure, there's a bullpen spot or two up for grabs, and a platoon opening at first base, but neither of those are projected to have much of an impact to the big picture. The most interesting competition will be for the back of the rotation. To the source!
"I think there’s going to be a great competition for the fifth spot in our starting rotation," Dipoto said, "and I think we have, minimally, six and perhaps up to eight or nine legitimate candidates.
There may technically be six candidates, but Mike Montgomery, Vidal Nuno, Joe Wieland, and the rest aren't much of in the way of competition for James Paxton and Nate Karns. Even with the field effectively narrowed down to Paxton and Karns, perhaps there shouldn't be a competition at all -- or at least not one that begins on an even playing field. Why you ask?
Karns can stay healthy
We all know about Paxton's injury history. Fragility has been a concern throughout his career, but it's become a real issue over the past few seasons. After starting 26 games in both 2012 and 2013, Paxton only made 13 non-rehab starts in both 2014 and 2015. Over the past two years, Karns has made 55 starts, and he made 26 more in 2013. Paxton has supposedly dropped 20 pounds in an effort to stay healthier -- which is great! -- but I wouldn't bet on Paxton making it through more a baker's dozen starts.
Standard Operating Procedure
Maybe Dipoto's truly a different breed, but it's a good rule of thumb that management will look to utilize those they bring in rather than those they are left with. Unless he's a Pete Carroll clone who doesn't give half a crap or secretly Boog Powell's father, Dipoto didn't trade for Nate Karns to send him to the minors or demote him to the bullpen.
Paxton can fill a bullpen need
The bullpen is currently filled with right-handers, some of whom may not suck! Charlie Furbush is a quality left-hander, but leaving him alone would be a shame, especially since he missed some time with injury last year. Mike Montgomery or Vidal Nuno may join him, but Paxton would be a more tantalizing option. If Paxton can throw 94 in the rotation, what could he do in one or two inning stretches? I don't want to make this lofty comparison, but could Paxton turn himself into something like Wade Davis? Karns could also make a good reliever, but his fastball would still be a couple ticks behind.
Karns may be flat out better
This is the most important reason, so let's address it last. Paxton has the upside of a bigger fastball and a more coordinated left arm, but thus far, the results haven't been there. Looking at the past two seasons, Karns has been slightly better according to metrics like xFIP and SIERA, as seen below.
Since Dipoto hasn't publicly broken out the sharpie, there will be a competition, but the outcome should never be in doubt. It should be Karns' job to lose, and that's for the best.