I think hitting hard comes from controling the path of your weaopon, I think any given guy can hit really hard, but are they centered?<shrugs> It's not mutually exclusive. One develops both power and control AT THE SAME TIME.
I just dislike the 'control over power' martial arts cliche since it seems to assume even the average martial artist will have Zen-like precision in the heat of a wild melee. In my experience, most if not all black belts in the sundry systems have a good measure of control. They can generally target something and hit it with a handful of hand or foot techniques. They're great at low-high paddle drills. However, a much few percentage of these people can hit their target with EXPLOSIVE power, even when the target is unmoving. To me that suggests a training paradigm emphasizing hard hitting might be called for.
Sean