It should be noted that Westbrook's numbers have steadily improved every year. His turnover rate his rookie year was 17.6, now down to 15.9, while his usage rate has gone up. His assist percentage, PER, TS%, steal percentage, free throw percentage, and points have all gone up. His dRTG has improved too since his rookie year, although marginally.
In the meantime, so has the overall OKC offense, from 99, to 105, to 110 in oRTG.
On the other hand, Rondo's TS% of .495 was his lowest since his rookie year. His rebounding rate (7.2) was the lowest of his career. His PER has steadily declined over the last couple years - in 2010-2011, Rondo was at 17.8, which puts him at average-to-solid...Westbrook's was at 23.6, which put him among the elite. Rondo's oRTG has also steadily declined over the last three years, from 114, 111, to 104 this year. His dRTG has seen a marginal decline, although its such a fluky stat that it's tough to read into it at all.
Rondo also posted the highest TOV% of his career (24.3), while Westbrook posted the lowest of his (15.9). Now, some posters have suggested that this is a result of Rondo being more of a passer and being more likely to turn the ball over since TOV% is directly linked to usage. This may certainly account for some of the disparity. I would also suggest that Rondo's inability to score or unwillingness to also increased his turnover tendencies that led to poor decision making, similar to what we see from Westbrook every now and then.