per 36, Jefferson has basically been a 20/10 player since he left Boston
The problem is Jefferson is not nearly as good on offense as people like to think he is. Everyone goes on about how good he is in the post, but when you look he shoots at a BELOW AVERAGE percentage from the post, the block, and in the paint.
He "looks" like he's a good scorer because he has some aesthetically nice moves, but he actually is below the league average at converting those moves into points. He takes far more shot attempts than his paltry shooting percentages should allow for.
He is certainly overrated on the offensive end. That said, he is a good rebounder and a decent defender. He just is not the post threat everyone makes him out to be - any smart team will gladly let Jefferson shoot his team out of a game from the post.
Now, Millsap is no offensive juggernaut, but he's efficient from multiple spots on the floor. All of his shooting splits are at or above the league average (except from beyond the arc, but Jefferson can't hit that shot consistently either). Defensively and on the boards, he is about on par with Jefferson.