OKC currently has a DRTG that is 6.6 points better than 2nd place. The next-biggest gap since the 1996-97 season is 2.6 points (2015-16 Spurs).
OKC is #1 with 104.1 DRTG, Houston is 2nd with 110.7.
It is hard to overstate just how absurdly dominant this historic defense is. If they had the worst ORTG in the league, they would still have a net rating of +4.2, which would be good for 8th in the league, just behind the T Wolves.