3. Converting Edwin Diaz to a reliever

See, I told you not all 5 moves were going to be trades. Instead, Dipoto gets credit for moving one of his few legitimate starting pitching prospects out of the rotation and into the bullpen. The result of such a bold move? The creation of one of the best relief seasons in baseball history and an insanely valuable trade asset.
The decision to move Diaz from the AA rotation to the bullpen was not a no-brainer. Diaz was (and still is) young and was on a good trajectory to join the Mariners rotation sometime in 2017. But the Mariners were somewhat surprisingly a playoff contender in 2016 and was in desperate need of bullpen help.
Dipoto’s decision to move Diaz to the bullpen, as well as the player development staffs tweak of speeding up his delivery, took Diaz from a 92-94 MPH fastball to a 96-99 MPH fastball with tremendous arm side run and he almost immediately became the best arm in the Mariners pen.
In his rookie season, Diaz appeared in 49 games, saving 18 and striking out 88 batters to just 15 walks in 51.2 innings pitched. Diaz followed that performance up with a good but not great 2017 before becoming nearly unhittable in 2018.
The decision to move Diaz to the bullpen was tremendous on every level. It helped Diaz reach the big leagues faster and significantly raised his ceiling and floor. It helped the Mariners win more games in the short-term. And it helped the Mariners to later capitalize on his tremendous value on the trade market.
Very rarely does one decision help the player in the short and long-term, as well as the team both in the short and long-term, but this decision by Dipoto did exactly that. Can you imagine if Dipoto hadn’t pulled the trigger and Diaz was kept in the rotation to see if he could finally develop that changeup?
Maybe he would still be in Seattle, penciled in as the #4 starter entering this season. Or maybe he’d still be in the minors trying to put everything together. But instead, Dipoto took a calculated risk and it paid off in every conceivable way.