2018: Lance Lynn
Why isn't Lance Lynn still on this team? Back in 2018, the right-hander was acquired from the Twins for Tyler Austin and Luis Rijo. Steal! Except he wasn't that impressive in his 11 games (nine starts). He finished with a 4.14 ERA and 1.33 WHIP ... but somehow had a 2.17 FIP. And nobody in this analytically-driven front office did anything with that information?
Instead, Lynn, who was bumped from the rotation to the bullpen against his wishes (we're spotting a trend, here!) left for the Texas Rangers in free agency. He finished fifth in the AL Cy Young voting in 2019 and then sixth in the shortened 2020 before being traded to the Chicago White Sox. In 2021, He earned his second career All-Star nod and finished third in the Cy Young voting. He experienced a bit of a backslide in 2022 due to a knee issue, but he was still better than anything the Yankees could've offered in the No. 4 or 5 rotation spots.
Here we have another instance where the trade was good and the decisions executed every moment following the trade were beyond poor. Since the start of 2019, Lynn has made ~$38 million. He'll make $18.5 million in 2023 and has a club option for 2024. Sub out any of Josh Donaldson, Aaron Hicks and/or Domingo Germán and you have a better team spending less money.
Technically not a "loss" on the trade, but we're still beyond bitter.