High pressure fluid injuries are significantly different, but we’re moving off track.
Let’s come from the other direction. Bludgeoning, slashing and piercing all do damage through the application of force. However, the damage they do is amplified and relise on a particular susceptibility of the victim.
Bludgeoning amplifies is force through rapid impact time.
Piercing amplifies is force through a sharp hard single point.
Slashing is more complex, but it amplifies with a sharp hard edge kinda.
But these ‘tricks’ to deal more damage don’t work on everything. For example bludgeoning requires ‘inelastic deformation’ before movement. I.e. a bat breaks a skull but not a tennis ball. I can see why crushing is put in this category, it recognises that damage is due to the susceptibility of the target to be inelastically deformed (bruised, broken bones, crushed organs w/e). Everything has an inelastic deformation point, put a tennis ball in a press and you can crush it. But in this case it’s not that the ball is susceptible to bludgeoning damage, it’s just that you have applied lots of force.
Same with piercing, the effectiveness of a spear is reduced by something that can distribute its force over a larger area. Which doesn’t matter if the ‘spear’ has a huge amount of force behind it. At which point it doesn’t matter if it was a spear with a sharp point or just a rod (or jet of fluid).