I am prepared to bet (unfortunately there is no way of testing my theory so I am on pretty safe ground) that the vast majority of children would much rather be one of 2 Toms or 3 Emilys in their year at school than the only Halcyon or Sequoia.
I also think that people are very disingenuous when they insist that they are choosing made up or off the wall names so that their children are the only one in their year. I have a Grace, who is one of 2 in a school of 1420 girls,and a Patrick, who is the only one in a school of 430 children. I don't know why people choose off the wall names, but uniqueness can't be the real reason.