4. Michael Kopech
Michael Kopech has had some flashes but he was ultimately a bust.
When Michael Kopech was acquired by the White Sox in the Chris Sale trade, the ceiling was incredible. He was seen as this flame-throwing star who could change the game as a starter.
As a reliever, Kopech has been pretty good. That includes this season. However, as a starter, he was pretty bad. He ended up being pushed back into the bullpen because of his issues as a starting pitcher.
This makes him a bust. You don't trade Chris Sale and expect relievers back in return. You expect a starting pitcher that can be borderline as good as Sale in his prime. That did not happen.
Like most of the players on this list, injuries and off-the-field issues have a lot to do with it. At the end of the 2018 season where he made his MLB debut, he had Tommy John. That forced him to miss all of 2019 and then he opted out of the 2020 season.
It got close to three years between pitches that counted for him. Again, he's a solid reliever but that makes him a bust based on the expectations placed on him when he was a prospect. It hasn't worked out as anyone had hoped.