You can see how much blocks he recorded. The improvements are not much visible in the game,and likely there aren't significant differences that can justify such a big salary gap.
Just because he didn't block a shot, doesn't mean that the SB on the player didn't have an effect on the opposing player. He could have altered some shots or lowered the percentage of the opposing player's shots, for example.
As for the improvements, they are to me, somewhat visible, and can only increase as more games are played.