Now you're making a distinction that I can sink my teeth into.You don't have to play "hard" to get a great sound. Velocity will get you there too.
When I think of a hard-hitting drummer, what I'm imagining IS that stick velocity at the point of impact. Terry Bozzio described his hard-hitting swings as semi-forceful stick swinging and wrist whipping, but that he also backed way off with the tension in his hands as he approached impact. You can actually see it in his playing, and it's cool to watch. He can get all the volume he could ever want, but he's letting the stick's velocity and momentum do all the heavy lifting. It's definitely not thuggish pounding.
Fun also to watch Vinnie's whipping motion on the stick. He can - and often does - pull some seriously explosive volume from his kit.
Contrast that approach with the tighter fisted drummers who literally pound their sticks into their heads and through their cymbals without ever letting up on their death grip. I doubt the volume is greater this way since the stick velocity is lower (tip travelling at about the same speed as the fist), and probably even less loud because of it.
Not wild about the second approach myself - not much grace in it. It's all about modulating the pressure of your grip during the swing - tighter grip for acceleration; looser grip for control and release.