Look at the dictionary meanings below. I have copied them from the New Oxford American English Dictionary (the application for the dictionary on my Macintosh laptop):
pedant: (noun) a person who is excessively concerned with minor details and rules or with displaying academic learning.
virtuoso:(noun) a person highly skilled in music or another artistic pursuit.
I'd have expected who is to be present in the case of virtuoso as well. Is the use of who is optional in this context?