I think the 100% is the efficiency with which they can use a particular type of Nen, not their level of mastery. More specifically, they can utilize the skills that they have learned in a particular category at maximum effectiveness. But that doesn't stop different Nen users of the same type from having a different degree of expertise. At the end of the fight, Kurapika determines that his enhancement abilities are just about enough to overcome the physical brawn of Uvo. This suggests that Uvo's mastery of enhancement alone is probably far greater than Kurapika's since he needed to use Chain Jail to forcefully activate Zetsu and seal up his aura before he could actually do any damage.
So Kurapika's specialization ability doesn't automatically make him a MASTER of all Nen types, it just removes any handicaps that normal users have in using skills outside their own class.