Rubs Are for When You Barbecue (Low and Slow), Not Grill.
Any discussion of rubs ought to begin with clarifying the difference between grilling and barbecuing.
Grilling is a fast, high-temperature method suitable for cooking, for example, burgers or steaks.
Barbecuing is a slow, low-temperature (typically 225 F) method you'd use to cook, for example, a whole pork shoulder or beef brisket.
This is a huge difference, and its misunderstanding leads to the misconception that rubs should be used for grilling. No! Rubs, either wet or dry, are for when you barbecue, not grill.