Hard to say what's changed the most for the Pistons. They've gotten a lot of improvement from all over their roster.
Drummond's ability to make a workable number of FTAs, Reggie Jackson not being a huge minus on the floor, Bradley's play, Harris is playing really well right now, etc.
Jackson improving on defense, and trying to take away passing lanes has been a godsend especially considering Jackson was a black hole on defense.
Drummond making free throws has also been a revelation. Jury is still out, whether or not Drummond can become more aggressive, and force more fouls. Also with them trying to adapt to the pace and space, their lineup of Jackson, Bradley, SJ, Harris, (who has been lights out offensively,) and Drummond has been a great lineup defensively.
I still am convinced the Pistons messed up not going after Bledsoe.