Part 1, what do about the Offense?
The Cardinals of the last two seasons have lacked thump from their lineup, having the 4th lowest slugging % in the MLB this past season. Overall their lineup was bottom ten in baseball in OPS+ and having the 12 worst WRC+. The Cardinals do however possess the best defense in baseball by DRS. Many people this offseason will see the disappointing outfield offense as an area to improve. However, I believe that adding in the outfield is a mistake for the Cardinals. Despite all the worry about his offense Harrison Bader managed a good 113 WRC+ and is quite possibly the best center fielder in baseball. Tyler O'Neill struggled at the plate but he significantly cut his strikeout rate and improved his walk rate, much of his failure was likely due to a .189 BABIP. Combine that with the facts that he is an elite defender, has elite speed, and had great minor league numbers and I see no reason to move on from him. Dylan Carlson is one of the best hitting prospects in baseball and showed how good he can be over the last two weeks of the season. Add in Lane Thomas who is a very good option to be a fourth outfielder based on past production, his defense and his speed, and I believe you have an outfield that could see a lot of internal improvement next season while retaining its elite defense.
So how do the Cardinals improve without adding in the outfield? Well I believe the Cardinals could improve their offense in three ways, add a true DH, upgrade at 3rd, and addition by subtraction. In reverse order I will start with addition by subtraction. You may noticed above I did mention Dexter Fowler, for good reason he doesn't fit with the narrative he is old, unlikely to improve at the plate, and sucks at defense. Now for the reasons above and his 15 million dollar salary for 2021 he is extremely hard to trade. However he is still a roughly average hitter and if the Cardinals were to retain 10-12 million dollars, they could trade him to a outfield needy team like Cleveland for a lottery ticket prospect. The next addition by subtraction is fairly easy don't re-sign Matt Weiters. Over the last 2 seasons he has a 76 WRC+ while simultaneously being a horrible defensive catcher. This frees up playing time for Andrew Knizner who based on minor league numbers is a better hitter who is younger and it is very unlikely that he is a worse defender. The final way the Cardinals can add by subtracting is to trade away Matt Carpenter. His 84 WRC+ and poor defense at age 34 is not the kind of player a contender should roster. He may bounce back, but the Cardinals can not afford to take that risk. How do you trade away Carpenter? Well that ties into my second area where the Cardinals can improve next year, 3rd Base
In 2020 the Cardinals primarily played Tommy Edman at 3rd Base, who based off the last two seasons is roughly a league average hitter, who is extremely fast, and plays pretty good defense at 3rd base. In 576 PA he has been worth 4 fWAR. So you may ask why would you try to replace Edman. There are two main reasons to do so he doesn't project to be as good as his 2019 numbers suggest, and he is extremely versatile. While their has been much complaining about Edman in the outfield DRS, OAA, and zone rating all suggest he is an above average defender there. Combine that with good defense at 3rd and 2nd and being an average SS and you have the perfect super utility player and an easy opportunity for him to get 400-500 PA spread across different positions. So how am I going to upgrade 3rd base. Arenado? Bryant? Turner? While all 3 are intriguing options they each have significant issues, for Bryant and Arenado the acquisition price is likely going to be too high in prospect capital and for Turner he is 36 and his defense seems to be eroding. Instead I think the Cardinals should trade Matt Carpenter, Angel Rondon, and Elehuris Montero for Kyle Seager. Seager who is 32 and his best days seem to be behind him. However the last two years he has managed a .240/.333/.456 slashline good for a 113 WRC+ combined with his still above average defense he has been worth 4.5 fWAR in 691 PA the last two years. He is signed through 2021 at 18 million dollars with a 2021 team option that becomes a player option for 15 million dollars. So in 2020 he costs the same as Carpenter and if Carpenter's 2021 option were to vest Seager's option is 3 million dollars cheaper if he stays. Seager is great stopgap at 3rd until the Nolan Gorman or Jordan Walker is ready. To get the rest of the deal done the Cardinals throw in two pretty good prospects in Montero who when healthy looks like a potential middle of the order bat, and Rondon who projects to be a 3rd or 4th starter in a few years. Seager may cost more in prospect capital but he won't cost the Cardinals any of their best prospects like Gorman, Walker, Carlson, Liberatore, or Thompson. He probably also won't cost the Cardinals any of their young MLB talent, making him a great acquisition for a team that should be trying to get better while not sacrificing what appears to be a bright future.
Another way for the Cardinals to improve the offense without sacrificing future value or defensive value is to sign a free agent DH for 2021. The best option at the DH position this offseason is easily Nelson Cruz. Cruz should have more suitors than last time he hit the market. However given his age and what he got last time from the Twins, they Cardinals should be able to sign him for a 1 year deal with a team option at roughly 20 mil/year. While Cruz will be 41 next season over the last 2 seasons he has managed a 163 WRC+ and 164 WRC+ respectively, all while maintaining excellent contact quality. This makes him a strong bet to at the very least manage to be a very good if not elite hitter next season. These moves combined with extending Yadi on like a 2 year 10 million dollar a year deal give the Cardinals a lineup something like this.
1. 2B. Kolten Wong(L)
2. RF. Carlson(S)
3. 1B. Goldschmidt(R)
4. DH. Cruz(R)
5. 3B. Seager(L)
6. SS. Dejong(R)
7. LF. O'neill(R)
8. C. Molina(R)
9. CF. Bader(R)
On the Bench you have Thomas(OF), Edman(IF/OF), Knizner(C), and whichever player out of Sosa, Ravelo, Williams, or Shrock impresses the most in spring training. Use Edman as Super utility spelling anyone and everyone in the infield and outfield either by direct substation or say by playing LF/RF with O'neill/Carlson in Center to replace Bader, same with playing 3B base with Seager at 1B to replace Goldschmidt.
After this offseason the Cardinals still have a team that should be fantastic defensively in both the infield and outfield while removing overpaid veterans, adding significant offense, and allowing for playing time for the young outfielders. The Cardinals may not become an elite hitting team but they could become well above average while keeping the great defense. The cardinals also retain the potential for a great offense with possible in house improvement for O'neill, Carlson, Bader and Dejong.