These rankings are massively flawed. Gabby had a solid rookie campaign but Diamond was clearly the more impactful player of Chicago's rookies, so right there I have to object.
Diamond had more points, rebounds, and assists per game than Gabby. But Gabby finishes higher under this system because she had more blocks and steals and fewer turnovers and fouls.
For some reason these stats only go through 7/31. Looking at the final stats, Diamond actually finished with more blocks than Gabby even though the difference is negligible (10 vs. 8). Gabby actually fouls more frequently on a per-minute basis than Diamond (3.0 fouls/36 vs. 2.8). So the areas where Gabby is better are really just turnovers and steals.
For two players who both played a substantial amount, per-minute stats are much more instructive, in my opinion. Now compare:
Per 36 minute stats:
Diamond - 18.2 pts, 6.2 reb, 2.8 ast, 1.4 stl, 0.4 blk, 2.6 tov, 2.8 pf
Gabby - 11.4 pts, 6.7 reb, 2.6 ast, 2.6 stl, 0.4 blk, 1.8 tov, 3.0 pf