I am definitely the Singles Specialist. In fact, in 3 years of USTA play, in Adult Leagues I have played 36 singles matches, and I have never been put in a Adult League lineup in doubles. The only times I get to play doubles is in Combo and Mixed. I am a decent doubles player, but I greatly prefer singles, and my teams have been perfectly happy to put me in singles almost every match.
One person that is missing though, the Talented Malcontent. This is the person who is one of your best doubles players, but for various reasons this person refuses to play with some others, or some others refuse to partner with that person. Usually because of arguments instigated by the Talented Malcontent, or backstabbing done by the Talented Malcontent. Its the person who you would rather not have on your team, but you are drawn to inviting them because of their talent. The Terrell Owens or Rasheed Wallace of recreational tennis.
While I am not one of the Talented Malcontents, I am very competitive and used to a singles mindset, and I know I am guilty of being unable to hide my body language and eye rolls when my partner messes up in doubles. That has gotten me into slight trouble on my teams.