Diaz played all last year at age 21. His total at AA at age 21 was 285/392/449/841 OPS, if you want to be a homer and exclude Bowie cause he was changing his mechanics or it's tough to change orgs or whatever he was 314/428/477/905 at Tulsa. He's been anywhere from the 30s-70s in the top 100 prospects in baseball. His wRC+ was 152 for Tulsa and 106 for Bowie.
In his age 21 season Adam Jones got to the majors for about 40 games (he also did at age 20 for a similar amount). His prospect rankings prior to that year seemed like 20s-40s. In AAA at age 20 his line was 287/345/484/829, and at age 21 it was 314/382/586/967. His wRC+ was 117 at age 20 in AAA, and 144 at 21 in AAA.
Already you can see they were different kinds of players. A lot more walks for Diaz, more power for Jones. Jones was better at higher levels. Jones' stats are PCL, generally higher, but wRC+ should account for league averages and park and stuff he did fine at AAA age 21, while Diaz also did a bit better at AA Tulsa at age 21.
What's all that mean? I have no idea. Jones was better at higher levels, but they were also different kinds of players. Two ifs: if Bowie was just an aberration and if Diaz develops power, that will be very nice. He has shown a good eye, so if he could approach Jones-like power that would be really exciting.