It’s an NBA truism that defense wins championships. Anyone who watched this year’s finals was reminded incessantly that the Celtics and Warriors were #1 and #2 in defensive efficiency in the regular season. Even casual fans can tell you that 19 of the last 20 championship teams were top-ten defensive teams. But there is less to those facts than meets the eye.
One issue is that an arbitrary ranking cutoff can be misleading. Sometimes the 10th best team is a lot better than the 11th best team, in other years the difference is rounding error. But the bigger problem is that there are simply too few championships in modern NBA history to establish any reliable pattern.