That is all quite fascinating, indeed. For certain values of "fascinating." How has it translated to championships?
I can play it your way. In the entire history of the NBA's three-point shot, only
two six teams have won a championship while leading the league in
three-point attempts defense: the 1986 Celtics, the 1996 Bulls, the 1999 Spurs, the 2000 Lakers, the 2005 Spurs, the 2008 Celtics. The best defensive team only wins 17% of the time over that span. So how has
defense translated to championships?
I mean, according to your original measure defense has translated only about three times better than three point shooting. But I'd hardly go out and suggest that playing defense isn't worthwhile because only N teams were the best at defense AND won it all. Better defense makes you better, right? I would certainly say so. Shooting more three pointers also correlates with you being better. Not as strongly as defense, but it's a very real effect. You can try to wish it away if you want, but the fact is that the percentage of three pointers is still rising. Teams are doing it because it works. I showed you the plot that demonstrates that it works. And smart teams are going to keep shooting threes.
10 teams out of 240 that finished Top 5 in three-point attempts got out of the second round, in fifteen years. I don't think we're going to be able to come to an agreement on any definition of "better" that provides for perennial first-round-and-out/second-round-and-out teams to be classified as such.
Your 240 denominator (the number of teams in the playoffs) is not the right number to use.
There have been 75 teams that finished in the top 5 in three point shooting in the past 15 years. I'll take your word that only ten made it past the second round. That's 10/75, or 13.3%. There are 30 teams in the NBA, and each year four of those make it past the second round. That's 4/30 or ... 13.3%! Teams that shoot the most threes have fared no better, and no worse, than all other teams.
If shooting more threes makes you slightly better, why hasn't it translated into better results by this measure? Maybe it's just a small sample size. Maybe it's bad luck. Maybe the teams that beat them also tended to be very high in three point attempts (say, 6-10) and there wasn't much difference. Most likely some of the teams that resort to a lot of threes do it because they AREN'T good at other, hard-to-change things that make a team better (like defense) and increasing their number of three point shots provides them an easier, if not-as-effective way to get better. Not best, but better. And what's wrong with better?