I disagree. Cayenne pepper in soups and other dishes is a flavor intensifier, much like salt is. The trick is to use just the right amount. It has to be below the point where people can identify it in the dish.
Well, that's a different deal, it stimulates/irritates the taste buds and makes them more perceptive to the other flavors.
Black pepper does this too, but it also has a flavor. Cajun sauce, jalapeno sauces and juice, Sriracha and Jamaican Jerk sauce all have distinct flavors and heat.
Regarding that last one, the habernero has a distinct flavor as well, but you gotta be damn careful or you can ruin a dish.