Fann: A look at Mariners’ rotation that should be top 5 in MLB

The 2023 Seattle Mariners are a team will playoff aspirations that stretch beyond a mere wildcard berth. This roster has realistic goals of being a factor for the American League pennant given its top-end talent, up-and-coming youngsters and overall depth.

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But for all the warranted excitement about a lineup headlined by potential MVP candidate Julio Rodríguez, Cal Raleigh, Eugenio Suárez, Teoscar Hernández and others, this team’s strength remains within its pitching staff.

Seattle’s starting rotation should be among the top five in baseball with an upside of possibly being the game’s best. The list of teams with a better rotation on paper is brief and subjective. You could make a case for the Mets, Yankees, Astros and Braves. and maybe a few others are on par or even better than what Seattle has to offer, but that list dwindles rapidly when you consider the long-term projection of the Mariners’ arms.

Here’s a player-by-player look at Seattle’s expected rotation in 2023, their potential growth over the next two to three years and the prospects that are coming down the pipeline.

• No. 1 starter: Luis Castillo

The Mariners acquired a bona fide ace in Castillo at last year’s trade deadline, and his pair of playoff outings cemented him among the league’s upper echelon of dominant starters. Castillo is a power pitcher that possesses immense swing-and-miss stuff (10.6 strikeouts per nine innings in 2022), the ability to pitch deep into games and the demeanor to succeed in the playoffs (1.88 ERA and 12 strikeouts over 14.1 innings in two starts last October).

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He should be an AL Cy Young candidate in 2023 and beyond given he just turned 30 back in December. Having a full season of Castillo atop the rotation is a major reason why Seattle expects to close the gap with the Astros this season. Status quo is A-OK when it comes to Seattle’s ace.

7 Ks IN A ROW to start the game for La Piedra 🔥 pic.twitter.com/hBnTI8pdhq

— Seattle Mariners (@Mariners) September 7, 2022

• No. 2 starter: George Kirby

Speaking of getting a full season out of a front-of-the-rotation starter, that narrative is also at play with Kirby. And when discussing postseason dominance, Kirby may have been even more impressive than Castillo last October.

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Kirby pitched a scoreless ninth inning in Game 2 of the Wild Card Series to earn the save and seal a dramatic series win over the Blue Jays that sent the Mariners to the ALDS.

He followed with seven shutout frames in a win-or-go-home Game 3 against the Astros in the ALDS. Neither a hostile Rogers Centre nor a sold-out T-Mobile Park rattled the 24-year-old rookie. He was unfazed by any and all pressure of postseason baseball.

Now 25 and entering his first full MLB season, Kirby could be a dark horse Cy Young candidate. He’s among the game’s best strike throwers and still managed an impressive 9.1 K/9 rate in 2022. Status quo over a full season would be acceptable, but Kirby’s ceiling is much higher than that.

• No. 3 starter: Logan Gilbert

Gilbert is one of the top wild cards on Seattle’s roster. Is his ceiling a dependable middle-of-the-rotation starter or can he consistently produce like a top-end guy? He’s gone under the radar compared to Castillo and Kirby, but I’m still bullish on Gilbert’s untapped potential.

The 25-year-old has been working on a splitter this offseason, a pitch that will likely play a factor in any meaningful step forward in 2023. He posted a 3.2 fWAR as a borderline All-Star in 2022, and it’s conceivable he finishes second behind Castillo in fWAR among Mariners’ starters in 2023. Seattle is hoping to see as much of “Walter” as possible.

FIRE US UP, LOGAN 🔥🔥🔥 pic.twitter.com/LbNHKo4ak0

— Seattle Mariners (@Mariners) September 7, 2022

• No. 4 starter: Robbie Ray

Ray was a disappointment in 2022 with a respectable but uninspiring 1.8 fWAR given he was Seattle’s prized free agent signing and the reigning AL Cy Young Winner. The walk-off moonshot Ray allowed to Yordan Álvarez in Game 1 of the ALDS only compounded the frustration towards the veteran lefty.

But the reality is that even if Ray doesn’t bounce back to his 2021 self (3.9 fWAR), Seattle’s rotation is deep enough to live with status quo. Very few teams in baseball expect their No. 4 starter to be a two-win player. The fear is that last year’s decline will only get steeper moving forward, and I think that concern is legit until proven otherwise.

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Over his last five seasons, Ray has posted ERAs of 3.93, 4.34, 6.62, 2.84 and 3.71. His career has hardly been the hallmark of consistency.

• No. 5 starter: Marco Gonzales

I was certain Gonzales would be gone by the time spring training arrived, but a trade market never materialized for the 31-year-old left-hander. Like Ray, Seattle is hoping for status quo. Being a replacement-level pitcher is serviceable in the last spot in the rotation. He posted a 0.1 fWAR in 2022.

Gonzales’ superpower has always been his ability to eat innings and battle through outings without his best stuff. Any uptick in production compared to last season would be a welcome surprise.

He did casually tell ROOT Sports this week that he added a slider to his repertoire, which adds a layer of intrigue to what he’ll look like in 2023.

• Injury insurance: Chris Flexen

Flexen is a curious case because of how deep Seattle’s pitching staff is, but he’s valuable insurance in case any starter was to go down.

The Mariners had incredible injury luck in 2022 as no starter missed a single turn in the rotation all season. That’s unlikely to happen again this year.

Flexen has actually been objectively better than Gonzales over the last two years with a 3.7 combined fWAR compared to Marco’s 0.6. But just like last year when the rotation was trimmed from six to five, it’s hard to imagine Gonzales accepting a role out of the bullpen.

My guess is that Flexen will be on the roster, and for more on that, last week I took a deeper look at the numbers game that will take place in Seattle’s bullpen during spring training.

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• In the pipeline: Emerson Hancock and Bryce Miller

Both young arms could make their big league debuts in 2023. Hancock should be Seattle’s No. 2 injury replacement in the rotation (No. 1 if Flexen gets moved), and Miller should arrive sometime midseason as another power arm out of the bullpen.

Miller is Seattle’s lone top 100 prospect, currently sitting at No. 98 on MLB’s list. He could join the rotation as soon as opening day in 2024. Hancock could be a full-time member of the rotation by that time as well if he continues to develop, though his time in the minors has been a bit turbulent with an ERA that has climbed each season.

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