Well, the scenario that prompted this thread (correct me if I'm wrong OP) was the rumor that a deal for Cousins was in the works. Sully's a good rebounder, but DMC is even better.
Although you are right, the difference is actually quite small. And, in fact, Sullinger is currently rebounding better than Cousins did during HIS rookie campaign. The trick is to look at rebound percentages, not totals ... the latter is a function of minutes played, the former is purely a function of skill.
Sully: 17.6% TRB, 12.7% ORB, and 22.4% DRB.
Cousins, this season: 18.9% TRB, 12.8% ORB, and 25.4% DRB.
Cousins, rookie season: 17.2% TRB, 10.4% ORB, and 24.4% DRB.
So Cousins has a slight edge on defensive rebounds, but by a slim margin, whereas Sully has the edge with offensive rebounds, by an equally slim margin. They are comparable rebounders.
In fact, for those of you who like Cousins and his development so much, compare the REST of Cousins' rookie year with Sully's. Remember, you can't look at TOTALS, because Cousins got 10 more minutes per game than Sully.
Cousins: 43% shooting (TS% = 48.4)
Sully: 47.1% shooting (TS% = 51.9)
Cousins: 68.7% free throw shooting
Sully: 76.1% free throw shooting
Cousins: 18.5% turnover percentage (percent of plays ending in turnover)
Sully: 10.7% turnover percentage
Cousins: 2.1% block percentage (percent of plays ending in block)
Sully: 2.1% block percentage
Cousins: offensive rating of 94, defensive rating of 105
Sully: offensive rating of 110, defensive rating of 102
Cousins: 1.14 PPS (number of points generated per shot attempt)
Sully: 1.17 PPS
Sully, now, is better, or at least more efficient, than Cousins was as a rookie at almost every measurable level of basketball. The only difference is he gets significantly fewer minutes (which is to be expected due to the differences between being drafted to the Boston Celtics versus the Kings).
All the numbers indicate that Sully is a special player. And I think he has more upside than DMC, in all honesty, simply by virtue of not being insane. Everyone says Sully has great BBIQ, has anyone ever said the same about Cousins?