I think Mitchell has the higher ceiling, but the injuries are concerning and with Chourio likely locked in as this team's CF through what will be both Mitchell and Wiemer's primes, at least one of them is likely to be traded because they are both more valuable as CFs due to their defense. The Brewers could find a way to hoard all these young OFs, but they would be better off using that depth to bolster pitching or corner IF talent at the MLB level via trade, IMO.
I think both Black and Wilken will be in Milwaukee by 2025, and Black is knocking on that door already. If Black isn't a total butcher defensively at 3rd, Wilken could move over to 1B.