Disclaimer: I am a stat geek!
I believe that basketball is actually similar to baseball in that you can use statistical analysis to understand a player's "true" performance. After all, we track many things that basketball players do like rebounds, steals, fouls, points, etc, etc. This has many benefits like finding great "value" and giving your team a competitive advantage over others in a salary constrained league. (the dollar resources are unfortunately limited).
We saw an increase reliance in stats in baseball in the 90s (and arguably, thanks in part to the father of Sabermetrics - Bill James - the Red Sox have won two World Series) and I think we're beginning to see the same in basketball.
I think this is a good thing as it can give teams that take advantage of it a competitive edge.
There are some more "advanced" stats (like Win Score) that include defense although admittedly not perfect, they do a great job of measuring a player's overall performance.
Now, when we look at Win Score for the Finals, PJ Brown is dead LAST. He's had some good moments but overall he's played poorly. One can argue that playing him so many minutes when you could be playing someone else like Powe is not the best for the team. I don't see why anyone should get upset by that argument.
I loved watching PJ play growing up. He WAS an excellent player. Unfortunately, he's 38 years old now and he just is not as good as he was. He can still play, but I think what some of the posters here are saying is that maybe he should play less minutes so he can be more effective and give the Celtics a higher chance of winning.