True Shooting % isn't the end-all-be-all of scoring efficiency. It is one measure, and it has it's uses, but to say one player is a
better shooter purely because of TS% without thinking about what it is measuring is a little lazy in the analysis department. If DeMarcus (and Rajon) are shooting a better percentage from the floor and from three point line than IT yet both have a lower TS% what could be the possible cause? The only other factor is free throw shooting.
IT is excellent from the line. He has taken 363 free throws this year and made 326 (90%)
DeMarcus is above average for a center, but could still improve. He has taken 463 free throws and made 337 (73%). That's right at his career average.
Rondo as we all know is a poor free throw shooter. It's the worst aspect of his game (especially now that he has improved his three point shooting). He's taken only 119 free throws and made 69 (58%).
So... when you say that Isaiah is a better shooter really what you're saying is that he's a better free throw shooter and he gets to the line often enough (6.4 attempts per game) for his 90% shooting there to really impact the game.
Let's extrapolate a little more:
I've highlighted all of the relevant shooting percentages. Rondo is better from 3pt range, better from 2pt range, and better overall. Isaiah is a lot better from the free throw line (and he's 11th in the league in free throw attempts).
Typically what separates a star player from a really good roleplayer is that star players get to the line a lot. The only MVP candidate who isn't solidly in the top 20 for free throw attempts is Stephen Curry, but of course he leads the pack by a mile in 3pt FG attempted and made so he's making his living there. So there's a reason why stats like TS% and PER skew favorably toward players who take (and make) a lot of free throws. But this is where I have a problem -- all past history aside (because really that amounts to inherent bias) does it make sense to say that Isaiah is a
better shooter this year when Rondo is outpacing him in every category except free throw shooting?
None of this is meant to say that IT isn't good at what he does and there are marks like PER and TS% which do reflect his impact on the game as a scorer. Back to my original argument though, we had a problem here with Isaiah and DeMarcus because there weren't enough possessions to go around. Isaiah has bumped his usage % even higher this year to 28.8. DeMarcus is at an all-time high this year and leads the league at 35.4. It wasn't going to work. You could say that DeMarcus needs to shoot less and pass more, which is fair, but that doesn't mean we would be better if we still had Isaiah. DeMarcus does so much more than simply score the ball. He's also an intimidating defensive presence and one of the best rebounders in the league. If it comes down to one or the other, you have to go with the big man. And a PG with a lower usage (19.2%) and a knack for leading people into high percentage shots is the right kind of compliment to a high usage scoring center.