Yes and no. At mid you are prime ganking target, especially if the other team has a jungler. Also it is easy to over extend yourself and have one of the side lanes come gank.
But yes, it is best to have the carry go mid. LeBlanc is not really a team carry. No AP champs are. So while having LeBlanc in mid helps for early and mid game domination, it is not as wise in my opinion as having a true carry such as MF, Trist, Ashe, or Xin.
Side lanes can be easily handled if people would by wards more often. With two people in the lane, just putting one in the river bush to help prevent ganks and one in the edge bush to control that while laning is essential. Most don't do that however.
Also mid isn't as easy as you think unless you are playing MF. Even then it is not a guarantee. Last night I went mid as Xin against an MF and straight up owned her. That is not to say I can do that against an MF that really knows how to play mid, but being MF and going mid is not a guarantee that you'll do good if the other player is better.