In my experience, they don't even need to be particularly fast. Poke at a mauler or shielder with a pike or long spear and have him block it anywhere less than full extension and he can almost always just walk in and get a free hit on you. Even if you aren't still stunned you likely won't be able to do anything to fight him off if he's focused.
The stun from hitting an object is always long, with my dear pike it literally takes like 1.5 second before you can block again. Hitting an object with that weapon is a dead sentence if anyone is attacking you.
I hate when that happens. Accidentally go through a guy and hit the wall or the ground or something and you're done for. It's good that it punishes thrusting wildly but can really screw you.
Another thing to talk about when discussing the weird stabs and animations, and that's how you can go straight through a person (friendly or enemy) or even object, about 1/4 - 1/3 of the way through the animation with a pike or long spear, because of how long it takes for the actual hitbox to activate. Having it do full damage at the end of the thrust doesn't make any sense, so when should it hit? And why doesn't it already?