What he doesn;t tell you, at least on the Drupal end, is that enabling all those modules at once will make your "social media site" howl bloody murder and that creating a nice UI for them will do the same to you.

Word. Unless Drupal has changed in the last year or two (and it might have), the number of queries Drupal issues for any given page is O((u+n)*m), where u is the number of users being displayed on the page, n is the number of nodes, and m is the number of modules installed.

You can cache static pages, but the constant activity of a social network makes that impossible if you're logged in.

Basically, if you install even a few modules on Drupal it'll take a big dump all over your database.