In the most complimentary way possible, Wei-Yin Chen has been about the most average starting pitcher in baseball since he entered the league three seasons ago. That is no small praise considering the Orioles are paying Chen $16 million over those four years. Chen has been the most consistent starter on the O's staff this season, and he has sustained similar performance for every season he has been in the majors. He has been the same pitcher as when he entered the league, and it has worked for him.
Chen has not changed his pitch selection at all since entering the majors. While he relies on his fastball and slider primarily, Brooks Baseball identifies five pitches he throws more than 5% of the time, including his sinker, curveball and splitter (commonly classified as changeup).
How is he the most average pitcher? Over his career, he has a FIP- of 101 and xFIP- of 102, almost exactly league average. His strikeout rate has ranged from 17.6% to 21.7%, with the league average at 20.1%. His walk rate has ranged from 4.5% to 7.0%, with the league average at 7.6%. He has had below average ERA (ERA- of 92) due to a relatively low career BABIP of .288. Some of that can be attributed to the O's defense, luck and Chen's flyball tendency, but Chen might actually have the ability to induce poor contact (at least for this season). According to this study by Rob Arthur of FiveThirtyEight, Chen is the pitcher who has been the best at suppressing batted ball velocity this season. This is undoubtedly a tiny sample to base any conclusion on, but it is a positive sign at the very least.
While some fans seem resigned to the fact that Chen would leave in free agency this offseason due to his agent Scott Boras (especially considering the latest episode with Dan Duquette demoting Chen for the sake of roster flexibility), the Orioles could potentially receive a draft pick by offering Chen a qualifying offer. Just for comparison, Rick Porcello, who has had performed similarly to Chen, received an extension of more than $80 million over four years prior to his free agency. It seems almost certain that Chen would not accept the qualifying offer, given what others in his position have commanded in free agency.
If the latest demotion represents the final straw in Chen's decision not to return to the O's, we should at least appreciate the stability he has provided for the O's over these four seasons, which coincide with the O's ascendency to competence. Chris Tillman's disastrous season this year should give us a hint of how difficult it is to remain even average at the highest level of baseball.