I have mixed feelings about bullpens as a general rule.
On the one hand, relief pitchers are fungible, as they are often nothing more than pitchers with limitations in one form or another that make them not good starter material. It may be the lack of pitch variation for instance.
On the other hand, building a bullpen, imo, should start with choosing pitchers whose pitches are quality and who have had success with the most important rule of pitching, which is getting outs.
My issue with the Cardinals approach of building a bullpen in part with other team’s rejects is that other team’s rejects more often than not aren’t quality pitchers who are good at getting outs. Hence, that is why they are rejects.
If there are quality pitchers in your system that aren’t starter material then by all means put them in the bullpen.
However if you don’t have enough quality pitchers in your system, then you acquire them through trade or free agency. The Cardinals should do more of that and less of shopping in the Clearance Aisle.