A dark side of the Mariners' 2025 success is already revealing itself

The Seattle Mariners spent 2025 proving they could be one of the sport’s model organizations on the field. They survived injuries and finally looked like the kind of operation that could stack contention windows instead of chasing one-off miracles. 

But as soon as the season ended and the industry descended on the GM Meetings, another reality came into focus: when you become that kind of operation, everyone else starts shopping in your dugout and front office. The “success tax” isn’t just about payroll. It’s about losing the people who helped build the thing in the first place.

Over the span of a few days, the Mariners watched three pillars of their infrastructure get pulled into bigger roles elsewhere. 

Mariners’ 2025 success is already costing them key voices on the staff

Andy McKay, the longtime internal architect of Seattle’s player-development and mental-skills machine, is headed to the Guardians’ staff as field coordinator. Bullpen coach Tony Arnerich is following him to Cleveland as Stephen Vogt’s bench coach. Third base coach Kristopher Negrón is taking a bench coach job with the Pittsburgh Pirates, sliding in as Don Kelly’s right-hand man. All three moves are wins for the individuals involved and a compliment to the Mariners’ operation. They’re also the exact kind of hits that make it harder to “run it back” in 2026 with the same cohesion that carried Seattle through so many tight moments this past season.

McKay’s departure is the easiest one to miss on TV and the hardest one to replace in real life. He wasn’t listed on the Mariners’ staff card in 2025, but for nearly a decade he’s been at the center of how the Mariners teach baseball and build culture. Brought in early in the Dipoto era, McKay blended mental-skills work, cross-disciplinary development and accountability into a language the entire organization could share, eventually rising to assistant general manager and vice president while still pushing to get closer to the dugout. 

Now he’ll get that dugout role in Cleveland, overseeing on-field work for a Guardians club that clearly decided Seattle’s secret sauce was worth importing. The Mariners still have smart people in player development, but removing one of the main translators between the front office and the clubhouse leaves a real leadership void.

Negrón’s exit is easier for fans to feel because they’ve literally felt his presence from the seats. The former utility man went from retiring in 2019 to managing the Triple-A Tacoma Rainiers in 2021, leading them to a Triple-A West title and earning Manager of the Year honors. That wasn’t a fluke; players raved about his communication, his preparation, and his ability to have hard conversations without losing the room. 

The Mariners rewarded that by moving him to the big-league staff as first base coach in 2022 and third base coach in 2025, even handing him the keys for a brief stint as interim manager when Scott Servais was sidelined with COVID in 2022.

Around T-Mobile, he became the rare coach fans actually talked about, whether it was for the way he kept players locked in or the way he wore cleaner, rarer sneakers than half the crowd down the lines — often trading nods and shoe comments with people in the stands. 

That kind of connection and credibility doesn’t show up on leaderboards, but it matters. Now, instead of helping the Mariners squeeze extra value out of their roster, he’ll be sitting next to Don Kelly in Pittsburgh, tasked with helping a young Pirates team grow up.

Arnerich’s move is another hit to the connective tissue that made Seattle’s staff work. A former catcher with a long track record in college and pro ball, he joined the Mariners’ organization a decade ago and worked his way up through the development side before landing on the big-league staff as a hitting coach and then as bullpen coach and catching coordinator. 

His fingerprints were on everything from game-calling improvements to the way young pitchers adjusted to leverage roles. When Cleveland went looking for someone to sit in the seat right next to Vogt, they didn’t just hire a random bullpen coach — they poached the guy who already shared a language and history with their manager from their shared time in Seattle. The Guardians get instant trust and continuity in their dugout. The Mariners now have to rebuild that trust chain between their arms, their catchers, and the voice running the bullpen.

Publicly, Justin Hollander has framed these departures the way good organizations usually do. This is, in his telling, the cost of doing business when you’re viewed as a place that develops both players and staff the right way: other clubs notice, and people get chances to climb the ladder elsewhere. There’s truth in that, and the Mariners should be proud that their people are in demand. 

But it sits awkwardly next to the front office’s stated priority of keeping the 2025 group together as much as possible. You can bring back most of the roster. You can keep Wilson in the big chair and run back the core. What you can’t do now is fully recreate the exact mix of voices, routines and relationships that helped pull this team through the grind.

That’s the dark side of the season the Mariners just had. The better you are, the less control you have over who gets to stay. Seattle has earned enough benefit of the doubt that fans shouldn’t view this as an automatic step backward, but it is an early stress test for an organization that wants to turn one breakthrough into a sustained run. The hires they make in the coming weeks will say as much about their 2026 chances as any trade rumor or free-agent splash. If the Mariners want their “success tax” to feel worth paying, they’ll have to prove they can replace not just titles on an org chart, but the trust, communication and shared vision those departing voices helped build.