Picking two complete outliers like Dikembe and Lou Williams is a pretty flimsy argument. In that case we should have held on to Stauaskas in case he became the 2nd ever 31 year old to score 20ppg for the first time.
Stats don't always tell the whole story but they don't lie either. Take a look at the top DRPM players in the league
http://www.espn.com/nba/statistics/rpm/_/sort/DRPM
One thing about defensive statistics is that they weigh heavier for big men but you can see that pretty much all these players are considered top notch defenders. You won't find a King who played full time on the list until you get to Koufos at the 123rd spot. You won't find Lavine until you're a few hundred players deep. These lists don't have good defenders at the bottom. Basketball is obviously a team game so if you want to compare him against his own team, go ahead. He's still going to be near the bottom of that list as well.
People tend to rely on their eye too much when evaluating defense. A player like Bogie had defensive moments where he trapped and ball hawked guys and looked extremely impressive. That sticks out in peoples minds and they wind up thinking that Bogie is a good defender but if you pay attention to him over the course of a year, he was below average. It's just that his impressive plays stick in your brain and his bad plays don't register as memories.
I don't know of a single good team out there that has bad advanced stats and I don't know of a bad team that has good advanced stats. They aren't 100% foolproof but they don't lie.