Once upon a time, you didn't have to be a superstar to get away with releasing a solo single. Now, not only does every other song feature another artist, but it's usually one of the same handful of artists every time. Not that long ago, the game was ruled by stingy collaborators like 50 Cent and Eminem, who worked primarily with their inner circle of labelmates and only occasionally with outside associates.

But that all changed in the Lil Wayne era, when pretty much every major label artist could get a Lil Wayne verse on pretty much any single, and nearly all of them did (or a T-Pain hook, or more recently, a Chris Brown or Nicki Minaj feature). Not only has this one-size-fits-all A&R approach made radio more homogenous, it's also flattened out the differences between artists, reducing most breaking and mid-level MCs to whatever qualities would work best on a song with Drake.