Pro: They do not have to roll the dice on their pitching depth until injuries or development forces them to
I only briefly touched on this earlier, but this was more so in regards to how detrimental an injury to one of their offseason acquisitions could be if they only focus on adding one or two starters to the rotation. This point has more to do with the dependence on their pitching depth as a whole.
It's inevitable that they'll have to use their starting pitching depth throughout the season in 2024, but adding three starters ensures that the top end of their depth is stronger than it would be otherwise. If Thompson and Hudson, for example, have to replace someone like Matz and one of their acquisitions for stretches, that is much more manageable than if they are asking Rom, Liberatore, or someone else to do so.
Again, the names are not as important as the point here. Whoever arises from the Cardinals' young pitching group as their top options is going to be much more impactful as injury replacements than being fully relied on to run as their fifth starting Opening Day. Their top need this offseason is the front end of the rotation, but the quality of the pitching depth they can collect will have as much of an impact on the 2024 regular season as the quality of their front-line pitching.