In the past 18 seasons, just three teams have moved into the defensive top 10 after finishing in the league’s bottom three the prior year. Half of those teams finished 25th or worse the following season, and nearly a quarter (13) finished in the bottom troika again, a half-dozen of those finished last, half of those repeating. So historically speaking, the Cleveland Cavaliers are as likely to have the worst defense in the league as a top 10 defense.
To be sure, there’s a natural regression to the mean. On average teams improve their defensive rating (according to NBA.