User blog comment:12th Supernova/Chapter 793: Bad News and Bad Translations/@comment-62.44.135.238-20150709140516/@comment-24.235.56.170-20150709155640

It's kind of like the British governing system. The PM controls everything, but technically, the Queen still has the power to overrule or change anything she wants on a whim.

The Tenryuubito just have more frequent and more insane whims. The Gorosei are still effectively in charge, but they have no choice when it comes to accomodating the Nobles.