I often define the alternate rotor, new pads and ss hoses packages as a 'brake enhancement' because that's what they do. They make the best of stock items. Or nearly stock if you reference a slightly larger rotor perhaps.
On the other hand the BBK market is more clearly defined by the fit of multi piece hats/rootrs, alternative calipers- either fixed or floating, and usually alum bodied. Also included are the common hoses and pads etc.
Not that everyone needs the second level. But a BBK is generally comprised of larger items for both more mass, less weight and more durable use. Some are also more flexible in sizing, caliper offerings and pad choices than the enhancement kit.
