Graphene in by itself is highly limited but when combined with others, its enhancements become notable. In the case of the carbon fiber for the driver, its more likely to be added to the resin solution used in the forming cone and fills in gaps in which remaining resin would typically remain. My expectation is the stiffer cone aided in pushing the cone breakup a bit further out.
The issue that remains crucial with graphene is methods of its application. A few years of experimentation were required to optimize the application of graphene to improve rubber products such as tires and shoe soles. In rubber tires, it resulted in improved strength in the rubber without reducing other performance areas like compound grip. In some respects, it improved grip performance as the lattice aided in maintaining is structural shape of the tread pattern under load. This is often called tread squirm.
BAC's wheels used on their Mono race car and some experimental bike frames achieved a 20% reduction in overall mass without loss of overall modulus of the finished product. You might even see its application in cabinets construction that use composite materials at some point.
This in addition to the broadened use of pitch based carbon fiber still leaves some development to take place in material science.
