The bullpen performance
During that same interview with 101 ESPN, Michael Girsch said that their biggest concern with the bullpen the rest of this season is figuring out if Ryan Helsley can get back to the player he was last season.
And he's right.
Sure, the performance of Giovanny Gallegos, JoJo Romero, Zack Thompson, and others matters a lot, but if Helsley is not that "stopper" that he was before, the Cardinals have even bigger issues to fix in their bullpen. Having a talent like Helsley helps stabilize the bullpen tremendously. It is much easier, and cheaper, to fill out the 6th and 7th inning roles than it is to find another closer for your bullpen.
The Cardinals will likely need to bring 1-2 external arms into their bullpen next season and then will be able to ride the first half of the season with those additions and their internal options until reshuffling the bullpen at the deadline (like all contenders need to do). But if Helsley is not the guy they need him to be, that's even more resources going toward the bullpen that I'm not sure St. Louis can afford to do while revamping their rotation.