Nolan Gorman could be in the majors by the end of 2021, and on deck to contribute in 2022. There is a clear overlap between him and the current players. His arrival is more imminent than Walker, the third baseman/first baseman the Cardinals drafted in the first round of the 2020 draft out of high school. Plenty of time for him to develop and see where that takes him. Could be that his frame and athleticism takes him to the outfield, keeps him at third, or moves him to first.
One thing about baseball -- have bat, will play.
There is no problem with a team having a top prospect at third base at every level. If you polled big league teams and asked them if they would want five of their top 10 prospects to be 3B at the top five levels, they would probably all take that. Good bet from that group comes a LF, a RF, and a 1B.
On Twitter the other day I was scolded for suggesting that Gorman could play LF because he looks like an infielder or something something something.
The list of former 3B moving to the outfield at some point is long.
And then there's all the 3B who also become standout 1B without the stop in the outfield, like Mark McGwire, Jim Thome, Mark Teixeira.
If the bat plays, the position will work out.
UPDATE: To avoid further confusion or correction, I should have been clearer in the top that I was going to mention the fluidity of the positions, and that's why I included Shannon and Chipper Jones. Shannon came from the outfield in to be a third baseman, and Jones went SS-3B-OF-3B. The larger point I was trying to make is there are many many examples of 3B and LF/RF overlapping.