I just looked at the shot block leaders in Knight. There seemed to be no correlation between speed and block shots.
Now, with that being said, blocks work weird.
First of all, the SHOT BLOCK rating is used to decide if the FGA is successful. Many people think of this as an "altered shot".
Then, on ALL READY MISSED SHOTS, the game decides if a block occurs. It then decides who blocked the shot.
In theory, the only real benefit of a block is that the offense doesn't have an opportunity to get an offensive rebound.