I wouldn't know. I'm the oldest of three, and none of us have a herd mentality. I also have three kids, and again, I wouldn't say that they are any more conformist than any only children I've ever met.
The individual child is in reality not more individualistic, unconventional,& nonconforming. In fact they are more like their parents as they are their only role models. They tend to conform and stick to rules and hence appear more mature compared to individuals with siblings. An individualistic, unconventional,& nonconforming person has nothing to do with the number of siblings but rather the makeup of that individual him/herself, the society they live in (some societies in the world demand conformity) and the people they associate with ( this would include friends from school, educational institutions and work crowd) and not forgetting the exposure one is subjected to daily say, media and foreign culture.