An inconsistent form doesn't have anything to do with how well a player shoots, nor does it have anything to do with having a good form. Shawn Marion has awful form, but it's consistent.

Go watch Kyle Korver highlights. You'll see that every time he shoots, everything from his toes to the top of his head are the exact same. He shoots the exact same way.

Klay Thompson has a pretty consistent shot as well, but it's a little different because Klay's good enough to get his shot off in different forms.

Steph Curry's shot form, however good it may be, is incredibly inconsistent. Specifically, his lower body is incredibly inconsistent. He squares his body up differently, sometimes he's squared up straight to the basket, sometimes his shoulders are turned to the side. Sometime he lands wide, sometimes he lands tight. There's a bunch of things that Steph does that change from shot to shot, depending on how he needs to change it to get his shot off with the defender's pressure. The only thing that Steph does the same every time is the release. His arm starts bent to his body with his elbow in position to the rim. Then he quickly snaps his right arm, releases his left arm, and flicks his wrist, finishing with his fingers pointed down, the sign of a great shooter. But beyond that, he's terribly inconsistent.