It has been written on a few times on this website and on other publications, but Giovanny Gallegos has and continues to be the St. Louis Cardinals best reliever in 2019.
Gallegos was acquired in the Luke Voit trade and is the only thing that is keeping it from being a landslide win for the Yankees. Gallegos and Voit are actually tied in WAR even though it may not feel like it.
The St. Louis Cardinals bullpen has been a huge strength for the team as they rank 1st in the entire NL in WAR and ERA all without Jordan Hicks at the back end of the bullpen.