I think the distinction between the Highbloods’ authority on Alternia and that of the Condesce is that while the land dwellers seem to have at least some form of complex government and various mechanisms in place to enforce that government’s laws, such as the legislacerators, the Condesce rules totally by force. She doesn’t have the legal authority to tell a lowblood or a clown what to do; but anyone who doesn’t do what she says can be easily overpowered physically, and even someone who can withstand physical attempts to silence them will be outlived in the typical hemospectral fashion and become irrelevant to her in the blink of an eye.

Sort of like the classic distinction between a parliament and a monarchic institution - but with the added threat of the imperial drones which, in the sense that they are much like attack drones employed by imperial powers on today’s Earth, also add the angle that the sea dwellers are alike to a foreign government occupying the land dwellers.