drating is a team thing, right? i'm not even sure if there is an individual defensive metric.
DRtg and ORtg can be computed on and individual and a team level. The team clearly influences the final number.
For what it is worth, I just look at how a player fits defensively with respect to teammates and his situation and do not use it compare players in vastly different situations.
Here, I read that Rivers is as good as Holiday (about) against lesser competition in short bursts. He may or may not be comparable over a longer period of time against stiff competition.