3. Mark Leiter Jr
It is impressive, if not bold that Jed Hoyer admitted that he did not fully address the bullpen last season only to address it this off-season with the signing of Hector Neris, who showed a dip in velocity with the Houston Astros last season.
Hoyer pinned the success of the Cubs' bullpen last season on the idea that Mark Leiter Jr's splitter would continue to get left-handed hitters out. It was a bet that paid off during the first half of the 2023 season while allowing the team to overcome the regression of Keegan Thompson, but the success of his splitter disappeared during the second half.
Leiter had a 8.59 ERA during the last month of the season and if the success of his splitter does not return in 2024, he likely won't last until the All-Star break.