5. True center fielder
While I don't necessarily think this is an issue for the Cardinals, it's never really seemed like they believed in any of their internal options to hold down the center field position this year.
Last offseason, Dylan Carlson seemed like the clearest option for the position, as they gave him the job after trading away Harrison Bader. Then after a Spring Training competition, Tyler O'Neill won the job. After injuries derailed the beginning of O'Neill's season, Lars Nootbaar took on the role. After Nootbaar hit the injured list, Tommy Edman seemed to impress the club in a big way out there. Now, they are back to running Nootbaar in that spot.
See what I mean?
While none of those options are plus-plus defenders in center field like Bader was, Nootbaar and Carlson do present the Cardinals with internal options. If the club sees Nootbaar as more of a corner outfielder though and does not see Carlson in their long-term plans, then an addition would be wise for the short-term.
I do mean short-term, though. Victor Scott II seems like the club's long-term solution there as he has torn up minor league baseball this year. The club's first-round pick this year, Chase Davis, has played exclusively in center field to this point as well.
So exploring a stop-gap option like Kevin Kiermaier or a reunion with Bader would give the Cardinals a great defensive center fielder once again to help their pitching staff and cover for some of the growing pains Jordan Walker has out in the corner.