A supersonic pellet is an aerodynamic disaster in flight. Everyone who shoots airguns knows this and has known to stay subsonic if they want to have decent to good accuracy.
Enter the Marketing Genius.....'Faster is Better' and, being humans and being susceptible to this ploy, the company who started it whom I will not name..cough, cough, gamo, cough...sold gazillions of rifles saying that they were faster than everyone else.
Marketing hype aside, the really powerful guns ARE useful for situations needing more ft/lbs but they normally work best with heavy pellets going subsonic. The more powerful, the heavier the payload they can shoot so the whole 'Horsepower Race' isn't totally useless.
Look at the velocities of the really accurate pellet guns. Normally around the low 500's.