The back of the rotation
Seattle finished fifteenth in the league last year with a 4.41 ERA from starting pitchers, perfectly league average. While they traded away Taijuan Walker, they signed another former Mariner James Paxton to fill that hole.
At the top of the rotation, the Mariners have Opening Day starter, Marco Gonzales, then they have the young Justus Sheffield, along with Paxton. The other half of the rotation is what I am worried about. The Mariners will run an unconventional six-man rotation and there are a lot of question marks with the final three spots that will be filled by Yusei Kikuchi, new addition Chris Flexen, and then one of Justin Dunn, Nick Margevicius, Ljay Newsome, or maybe later in the season prospect Logan Gilbert.
Kikuchi was brought over from Japan two years ago and is yet to have an ERA below 5, but he did show some promising signs last year. Chris Flexen is a bold and italicized question mark, as he struggled in the majors, but then was excellent last year in the KBO, which led the Mariners to sign him to a 2 year $4.75 million contract. That was enough to make him a shoo-in for the rotation, but not enough to break the bank if he struggles.
Then there is the group competing for the final spot, who all have their flaws. I broke down the competition for the sixth spot in the rotation here. The back end of the rotation could end up not being too bad, but for now, it looks like it may hold back the rotation from being one of the better ones in the AL.