There hasn't been enough time for most prospects traded away to prove anything. Some, like Guerra, have proven to be vastly over-rated, but some still show a lot of promise.
One has "proven" he belongs, but it's still too early to judge: Yoan Moncada hit .915 last year at age 24.
Here's a list of all the prospects traded by DD and their highest ranking on soxprospects.com. (Travis Shaw was no longer a prospect when traded.)
1 Yoan Moncada
1 Blake Swihart
3 Manuel Margot
3 Anderson Espinoza
5 Michael Kopech
5 Jalen Beeks
5 Deven Marrero
6 Javier Guerra
7 Luis Ax Basabe
9 Mauricio Dubon
11 Shaun Anderson
12 Wendell Rijo
13 Logan Allen
15 Santiago Espinal
16 Ben Taylor
17 Ty Buttrey
18 Luis Aj Basabe
20 Bautista Gerson
20 Carlos Asuaje
20 Stephen Nogosek
Some are already pretty much sure busts, but let's come back and revisit this list in 3-6 years.