Throwing a baseball hard is, essentially, a prerequisite to be in Major League Baseball. Yes, there are outliers. There always are. Yes, velocity itself does not fully explain what makes a good baseball. How a fastball spins and how it plays off a pitcher’s full arsenal are also important. However, all things being equal, throwing a fastball, well, faster is better than throwing it not as fast.
This is especially true in the realm of the bullpen. When you don’t have to have worry about saving yourself for pitches 80 through 100, and when you don’t have to worry about your full arsenal, you tend to focus on your best pitches and throwing the crap out of them.