Mariners' Bryan Woo still making case as MLB's most underrated ace

By now, the baseball world has been put on notice: the Seattle Mariners’ starting rotation isn’t just good, it’s a nightmare for the rest of the league.

One through five, this staff is stacked with arms, each capable of overwhelming hitters on any given night. Leading the group is veteran ace Luis Castillo, a battle-tested leader whose fastball-changeup combination sets the tone. But what makes this rotation truly dangerous isn’t just his frontline presence, but also the embarrassment of riches behind him.

Logan Gilbert, George Kirby, Bryce Miller, and Bryan Woo don’t simply complement Castillo. They challenge him for the spotlight. The biggest debate isn’t if the Mariners have one of baseball’s most dominant rotations. It’s who among the five has the highest ceiling. Ask five different analysts, and you’ll get five different answers.

One name in particular is forcing his way into that conversation with urgency: Bryan Woo.

Woo was better than you think in 2024

The 24-year-old right-hander has taken center stage in this friendly debate. And as we gear up for the 2025 regular season, his case is only growing stronger.

Mariners fans have been vocal in Woo's defense, questioning why he continues to be overlooked in national rankings despite his numbers standing toe-to-toe with the league’s best. Take away the names, line up the stats, and compare them purely on merit, and one pitcher finished 2024 with a 2.72 xERA. So did another. One of them was AL Cy Young Award winner Tarik Skubal. The other was Woo.

Despite starting the season with a limited workload , Woo’s 2024 campaign showed striking similarities to Skubal’s dominance. Skubal faced 281 more batters last season, but when looking at sheer performance on a per-batter basis, the gap between the two is razor-thin.

Even more fascinating, Woo hasn’t even unlocked his full arsenal yet.

Woo leaves batters discombobulated

In 2024, Woo made a name for himself by relentlessly attacking hitters with a 72% usage rate of his fastball and sinker. With minimal variance in his pitch mix, he pounded the strike zone, daring hitters who, more often than not, couldn't adjust.

"When he locks it in, the hitters when they get to first base, they’re like, ‘That’s different,’" Mariners catcher Cal Raleigh said of Woo's effect on hitters, via Seattle Sports’ Brock and Salk show.

That reaction speaks volumes. Hitters who are lucky enough to reach base against Woo recognize just how taxing their at-bats are, acknowledging the grind it took to get there. He’s not built like Gilbert, nor does he possess the length and fluidity of Kirby, but his deceptive low-arm slot and aggressive approach make him uniquely challenging. His delivery is uncomfortable, his stuff is heavy, and he’s only getting better.

Woo wasted no time making a statement in 2025, delivering a near-flawless first spring training start on February 28th. Facing the San Diego Padres’ regular lineup, he pitched 1.2 hitless innings, allowing just one baserunner on an error by shortstop Colt Emerson. It was a small sample, but a sharp reminder: Bryan Woo isn’t just here to fill out the back end of the Mariners’ rotation, he’s here to establish himself as one of the best young arms in baseball.

The league has been put on notice. Even as Seattle’s No. 5 starter, Bryan Woo is still an ace.