I think the best uses for the 3 CMSes i mentioned are as follows;
WordPress - blogging platform & simple websites
Joomla - small scale to medium websites
Drupal - Large scale web projects, it's much better at handling complex data.
Sure you could make a large complex social network using WordPress but that would be tremendously complicated, whereas that same task could be shortened if one were to use Drupal. I hope you catch my drift.
Insinuation - not at all; it is the widely used CMS in Zimbabwe, . Therefore Joomla sites have a higher to get hacked, if devs/ rather template pushers forget to secure it thoroughly.
Perhaps i misrepresented my case in the article.