The thin is that it's NOT weak. When you purchase .40 from a store, it's loaded to +P+ pressure levels, and often outperforms many similar sized cartridges which are at normal pressure levels.
The reason why it's called short and weak is because you can easily overpressure 9mm and get superior results, the russians do it after all. To talk least of overpressurizing the 10mm to get essentially rifle scale energies.